From Venice to Swiss Alps to Paris

Train (depart 8:20) Venezia S. Lucia->Milano Centrale->Speiz->Interlaken Ost->Murren BLM (in one day, about 7 hours)

Spend your days in the Swiss Alps in Murren or Wengen and explore that stunning area.

Take the Golden Pass (or just any regular train) from Interlaken Ost -> Montreux to see Castle Chillon. Spend the night in Montreux. Resume you travel next day Montreux -> Geneva where you'll pick up the high speed TGV directly to Paris (4-5 hours).

I would stay in Varenna as I suggested in your other thread. Hotels are less expensive than in Milan, and the lake is stunningly beautiful. Albergo Milano is our favorite, but there are other options as well.

From Varenna to Pontresina over the Bernina Pass is 3.5 hours. You could spend a night there, or continue to Luzern (another 4.5 hours via Chur and Arth-Goldau. The first option has three one-night stays in a row; the second gives you one night at Varenna and two in Luzern. That leaves you two nights for the Berner Oberland suggested by Tim---but note that early June is still early for the higher elevations there. You will however be able to take lifts like the Schilthornbahn if you wish to have a "peak experience".

Or you could skip the Berner Oberland and take the Golden Pass train to Montreux for the last two nights. This is at a lower elevation and should be quite nice at that time.

Thanks so much, Lola. (Also, thank you for your comment on my other thread--I deleted that post since in that one I mentioned routing through Austria and definitely decided against it, but I saved your comment!). Would you recommend Luzern over staying in a place like Wilderswil? I was thinking I could take the train over the Bernina Pass but then head on to Wilderswil rather than Luzern and spend a few days there, exploring Wengen and Murren. Then I would head to Montreux for two nights, then to Paris.

I am going to revise my earlier suggestion of the Bernina Pass route---it takes you too far to the east, out of your way. Take a look at this Swiss train map and you will see what I mean:

https://www.swisspasses.com/railpass/overviewmap_en.pdf

You could have fun on the way to the Berner Oberland by going via Locarno and Domodossola, on the Centovalli Railway:

http://www.myswitzerland.com/en-us/centovalli-onsernone.html?iPadCover

This would break up the long journey and give you a night in the lakeside town of Locarno.

And in case you would like alternative suggestions to the Berner Oberland (not sure what the weather and conditions are around June 1) I will suggest another car-free village called Bettmeralp.

https://www.aletscharena.ch/en/?season=summer

This is perched high above the Rhône Valley, on a south-facing slope ( sunnier than other aspects). It is detour from your route to Montreux and then to Paris. From Brig, you had East two stops (12 minutes, if I recall correctly) to Betten, the Valley station for the cable car up to Bettmeralp. From the village you have views across the valley into Italian Alps. From the ridge behind the village, you can see the huge Aletschgletscher, Europe's largest glacier, flanked by snowy peaks. If you walk to the next village, Kuhboden, you can ride a cable car up the Eggishorn and see all the way to the Jungfrau.

Another vote for the Centovalli Railway.