Vancouver BC to Victoria

Since your floatplane will be leaving from somewhere near to Waterfront Station you could just take the Skytrain to Waterfront and from there Gastown is quite close (just hang a left as you leave the building and you are pretty much there). It’s not a big area, but has some interesting shops and the steam clock. Then you could take the Seabus across the harbour and visit the public market there ( when you exit the Seabus terminal just turn right). These two combined would probably use up your six hours. The other option would be to go to Granville Island. You can catch the #50 bus to get there right out front of Waterfront Station. The bus doesn’t go right into Granville Island, you will have to get off at the stop under the bridge and walk about a block in to where the public market is (ask the bus driver to let you know where to get off) Again, it is a small area with the public market and a lot of other interesting stores, places to eat, or just sit by the water. When you exit the front of the train station, you will see a park across the street. If you walk straight across that park you will come to Main Street, and you will see the Skytrain line overhead. Just cross the street to the Station, buy a ticket at the machine and go upstairs and wait for the train that says it’s going to Waterfront. This ticket is good for 90 minutes if you choose to take a bus or the Seabus.

While I agree that Anita's suggestion of Gastown and the Granville market are great places to see, it does require walking and standing. We don't know what constitutes "minimal" for you and your husband to know if you can manage that or not.

I suspect both places may be busier compared to a weekday? When I was wandering around Gastown on Sunday May 4th this year it was incredibly crowded but some of the crowds related to that also being the day of the Vancouver marathon.

Given that it's Sunday, check opening hours for any public site you intend to go to. If your train arrives on time, you may need to hang around the train station or other public area until sites open.

I'm sure you will get other advice and suggestions.

I know you have booked your floatplane flight from Vancouver to Victoria. When I travelled from Victoria to Vancouver I used the Wilson's bus service - meet bus on the street behind the Empress hotel - bus drives to Vancouver Island ferry terminal, drives onto ferry. Exit bus to sit in comfortable chairs on ferry and enjoy the sight of the Gulf islands; get back onto bus when the ferry is almost at mainland ferry terminal; bus drives into Vancouver and stops at many downtown hotels. It's not fast though -entire trip is about 4 hours. I had never been on such a large ferry before so the entire process was interesting.

Looking at the Harbor website, it's $3/pound for overweight bags (with no guarantee they will make the flight), but they allow you to drop your bags off early and have them sent on an earlier flight (for the same $3/pound fee, if I read it right). That's what I would do, drop the bags off upon arrival. Then you're unburdened for your wait time.

If you are taking the Canadian across Canada, it can be days late, not hours late, getting in. Please google this. The passenger trains have to give way to all the freight trains on the track and it can make the passenger trains way later than they should be. There is a website that tells you where the train is now that can give you the idea. Mu husband and I took the train from Vancouver to Saskatoon which came in 6 or 8 hours late. It was a great trip and I didn’t mind the delay at all because we got two more wonderful meals on the train and we weren’t leaving Saskatoon that day so no stress about connections.
I wouldn’t be booking anything onward until you get there, if it was me.

I did this trip in 2019 (and of course, only once). My train was on time, but they often aren’t.

I would definitely have Plan B ready: is your flight changeable if you are late? (Biggest question) Will you be able to call to let them know if you will be late? How will you get to Victoria if your train is late and you miss your flight? And thus, will you have a way to book a last minute place to stay if needed?

If all goes well, you have asked the right questions. I did my trip differently - stayed in Vancouver, took the ferry to Victoria, and flew back to Vancouver on Harbour Air. So I’m no help for specific answers to your questions. Hopefully I am just helping to brainstorm questions for an unneeded Plan B!

Canadian shipping costs are often extremely prohibitive. I expect that the FedEx website will give an estimated price for shipping your excess baggage, but I would compare that to the $3/pound overweight fees for carrying on the plane. I did a dummy estimate plan and sending a 10 pound parcel to Victoria would cost $30 Cdn by ground...so no date and time guarantee. By air minimum cost to receive the next evening is $87. If you want first overnight delivery....$120.
Then of course there is the Sunday thing....as in Fed Ex here rarely has Saturday let alone Sunday options.
For all the hassle, just wear more layers and pay for the excess on the plane.
Looking at the Harbour Air location, you will be near the Canada Place Cruise Pier. You could wander inside for local West Coast art, and there is a sea wall walk just the other side of the air terminal.
There are a number of eateries all around the area, but I am mindful that you are on a budget. Last time I had a conference in the area, I shopped at Urban Fare just past the air terminal. A gourmet grocery, but you could pick up some items and picnic on the seating areas along the sea wall. Or there are McDonalds, Subway and Tim Hortons (a Canadian classic maybe like Dunkin Donuts...but better coffee) are all just by Canada Place.
If the weather cooperates, there of opportunities just nearby to people watch and enjoy the scenery.

To be fair to Via Rail, they do have disclaimers on their website that you should not book onward travel or activities the day your train arrives into your station.
https://www.followmeaway.com/things-to-know-train-across-canada/

You may have a lot less time to 'kill' than the official schedule would suggest.

If all your plans are not yet carved in stone, you may want to consider adding an over night stay in Vancouver.

Good luck

We just took Harbour Air last week and people are correct regarding that you can pay if you are over the weight, as long as there is room on the flight. The one we took was around the same time on a Sunday and was not full, so we would not have had a problem. I was actually over by a couple of pounds ( my husband was under, darn him) and they didn't charge me.

You could check out Cardero's which is close to the Harbour terminal for a breakfast/ lunch. It is close by. There are also some smaller little coffee places right by Cardero's if you prefer. The Harbour terminal also has a pleasant area to sit, coffee, snacks etc, although I wouldn't want to spend 5-6 hours there. But it does have nice views of Burrard inlet etc. I also suspect that if you arrive early you might be able to get on an earlier flight, but don't know for sure.

Changes by the Passenger:
More than 72 hours prior to scheduled departure time: Reservations can be changed to same tier, or higher. Passengers must pay for any difference in fare and $50 change fee.
Day of, up to 1 hour before scheduled departure: Reservations can be changed to another same-day flight on the same tier for same-day $75 change fee.
From the Harbour Air site..

Looks like a late arrival would likely add cost to the flight, but shouldn't be a total loss. ( as long as you are able to contact them ahead of time)

Dress for rain in Vancouver and Victoria in October. It will probably be light rain. The Sky Train is just across the street from the Train Station. The Train Station does have a small cafe, but it is no place to hang out. The station is a public space. Best bet with luggage is to take a cab or uber to the Fedex? We took the Sky Train but we had no luggage. Dress is very casual in this part of the world, just wear comfortable walking shoes. Gastown has several restaurants. You may able to store your luggage at the Harbour Terminal. You might be lucky, sometimes, it doesn't really rain until Halloween.