There is no passholder quota. Availability a day or two before is never an issue in Italy.

About your main question:

Verona - Padua is closed for 3 weeks in August*. High-speed trains will be rerouted via the Bologna outskirts. It's a much longer journey than usual (1h30 extra) but way better than replacement buses!

They are still figuring out the timetables, they should come out in a week or two. :)

*if you're curious: they're connecting the new high-speed line to the old mainline. Works to continue in the next years, few weeks/weekends at a time.

Thank you for the reply. I am seeing some schedules on the rail europe site now. It looks like there is a direct train at 8:13 from Milan Porta Garibaldi to Venice S. Lucia that will take 4 hr 29 mins. With my eurail pass there are good seats I can reserve in business class for a low price. Would you recommend this journey? There are shorter ones that require a change and cost much more.

Also, it looks like Milan Porta Garibaldi station isn’t too far from Milan Centrale?

Yes sure the 08:13 train would work. It should cost 13€ pp (+2€ for seat selection if you wish). Porta Garibaldi isn't far from the center and it has a subway station.

Yeah it's faster to change in Bologna but I'd rather stay on the same train and enjoy the scenery from the windows. :)