The International that travelled from Chicago to Toronto had either VIA equipment one day or Amfleet equipment on another day - back in the early days. There could have possibly been VIA or Amtrak power on the point with VIA or Amtrak coaches behind it - making it a mixed to a degree. But for the most part I think they tried to keep the revenue coaches either all VIA or all Amtrak. But there may have been some odd days of operating with mixed coaches - not sure. But again, you'd have to go back in the International's history.
The Adirondack ran with a ex-CP (now VIA) Skyline dome with essentially Amtrak Heritage equipment. Amtrak/D&H leased two Skyline Dome cars to operate on this service north of Albany - similiar to what is currently being done today with the Great Dome, but not on an every other day cycle like present.
I think VIA could probably lend their expertise to the fixing of Amtrak's single level Heritage equipment. But of course not much is left now - just the diners and baggage cars for the most part. But the Heritage crew cars could probably have went to Canada for an overhaul - and overhauled based on FRA standards - if Amtrak wanted to keep them in service. Now these cars were restored and put into service for the GAO office.....go figure. VIA probably could have taken some Heritage sleepers from Amtrak and restored them to FRA requirements - retention tanks and all, as is now operated with VIA's ex-CP stainless steel Budd cars (that Amtrak would dub Heritage equipment). It's too bad VIA and Amtrak couldn't have worked more closely together on its Heritage equipment. Obviously VIA had the "know how" as what Amtrak considers Heritage equipment basically makes up the backbone of VIA's long distance and some corridor train sets - VIA's Canadian most importantly!
VIA and Amtrak - two companies that should have worked more closely together. VIA sort of tried by "testing out the Amtrak Superliner." But the Canadians didn't really go for it. Restoring what is now 50+ year old Heritage equipment was the way they went. Then of course they added in some UK purchased rail cars VIA has dubbed the Renaissance fleet - coaches, sleepers, diners, baggage cars, transition car etc. Freed up ex-CP stainless steel Budd equipment on the route of the Ocean, while the Chaleur retained its Budd equipment, despite original plans to equip both trains with Renaissance equipment. Perhaps that was to come with the stored Renaissance cars that are not to be! Money ran out!