four countries in a month

You need to take a map and put some pins in it. Since you are starting in Barcelona, I would be tempted to fly to Rome and work my way to France and Portugal from there. Without any idea of what you like or don't like, it is hard to recommend a plan. You do have a lot of options.

...florence, venice then train to tuscany...

Is this an order you are contemplating? If so it sounds like you are considering visiting Venice on only one day as a day trip?

If that's true, please reconsider. You would be there at the worst time of the day - the best time is between dawn and breakfast and in the evening and night - and for such a short period of time you couldn't "get off the valley floor" as we used to say about Yosemite.

The other question is about the train to Tuscany? Florence is in Tuscany. So is Pisa. There are small towns, but they often either don't have a train - most are hill towns, certainly the most romantic ones, and hills and trains don't mix well - or if they do they are often well away in the valley and not always frequent or fast.

Can you help put a bit of meat on the question? I don't know anything about Spain but I certainly do the rest of the places you mention...

When is the trip?

Any of these countries are big and can easily absorb a month of your time independently. But I'll try not to discourage. You will only be able to get a cursory introduction to any of them, and keep in mind that every move is .5 - 1 full day, so I recommend grouping towns in a country, fly between countries and buy open jaw flights to and from home.

I find Rome2Rio to be a useful website for plotting sequence of cities/countries as it shows lines and you can quickly see where you will be overlapping and back tracking. It also gives the transport options and timing of the transit.
It might also help if you say where your cruise is taking you in any of those countries that you don't want to revisit.

we are taking a 14 day cruise to spain

Is this how you are arriving in Barcelona?
Or are you flying to Barcelona , taking a month to do the ground tour and taking a 14 day cruise at some point?

Is arrival in Barcelona and departure from Lisbon 'set in stone'?

A bit more detail about your trip would help you get some useful answers/advice.

Although Rome2Rio will usually provide accurate information about the type of transportation available between two cities, you absolutely cannot trust the travel times, frequencies and fares it displays. Even before the disruptions caused by COVID-19, Rome2Rio's detailed info was wildly unreliable. However, if you keep clicking through the website, you'll find the name of the company providing the transportation you're interested in and will be able to go to its website for precise information.

Is it a 14 day cruise plus a month of travel to four countries? Or is the cruise time included in the month?

Your message mentions Burgundy near the beginning, and again at the end. From the Burgundy region of France, are you planning to fly to Lisbon? From either Paris or Lyon, flights are about 2 1/2 hours. Train travel would take a lot longer, of course.

We love taking the transatlantic cruises and have one planned for October 2021 from Rome to Tampa.

You have one month to visit four countries. All are large except Portugal.

I suggest cutting down your countries to 2 or 3. You could easily spend a month in Portugal and Spain.

To do the big three in Italy, you need two weeks. The big three are Rome, Florence and Venice, with perhaps a couple of days to see Sorrento, Capri and Pompeii in the South.

If you are starting in Barcelona, just plan on visiting Portugal on another trip. We did two weeks in Portugal a few years ago where we did a 7 day river cruise on the Douro Valley, which is amazing.

Just visiting Spain would require 3 nights in Barcelona, 4 in Madrid (incl. day trips to Toledo and Segovia), 3 in Seville, 1 for Cordoba and 2 for Granada.

If you just do Barcelona in Spain and not Portugal, you could handle doing the Rhone Valley and Provence (that will take about 8-10 days) Don't miss, Vienne, Viviers, Arles, Avignon, Monaco, Les Baux, Cannes and St. Paul de Vence.

OH boy - we get to help someone else dream. We did something similar last year - in reverse. I'd suggest dropping Portugal this trip and head East. Since you wouldn't need to backtrack.
This gives you a tiny taste of the major cities/areas and will leave you wanting to come back for more.

After the transatlantic : I'm assuming will have a stop or 2 on Spain's coast and you haven't been to Barcelona.

3 nights Barcelona (disembark day and 2 more days)
Fly to Lyon - 4 nights (flt day + 3 days) {Burgundy Region} city and a day trip (train) to Beaune or Dijon
Train South toward Avignon (collect rental car in Avignon) - 4 nights (train day + 3 days) {Provence} (stay somewhere near there) - local day trips - probably too early for lavender but villages and ruins should be great.
Return car -train to Nice - 4 nights (arrival day + 3 days) {Cote d'Azur} - city and day trips - Monaco etc
Flight to Florence - Rental car at airport- 4 nights (Flt day +3 days) {Tuscany} Pisa/Sienna or small towns
Return car Florence (train station has a drop point for some) stay in city - 3 nights (car return day +2) city

Train to Rome (4 nts) then Venice (4 nights each) either order - depends on train schedules.
Fly home from either Venice or Rome.

This is 30 nights, if my math is correct. This would only give you a taste and is traveling quickly/fast but doable. If you wanted to slow down a bit more - I might drop Venice and save it for a later visit. Add those nights along the way to the areas you are most interested (? Burgundy since you mentioned it twice?) - every area/city could easily handle lots more time.

If you really want to have a stop in Portugal... Drop Venice and fly from Rome to Lisbon - use the 4 nights.. and home from Lisbon (TAP does have some great prices).

Have a great trip and happy dreaming - Let us know what you decide.

Trains from either Spain or France to Portugal are primarily slow and overnight. The best way to reach Portugal from anywhere else on your list is to fly (or to skip it).