The late night YYZ-YHZ flights are "always" delayed, but that isn't something you can bank on. (I would not assume the MAX being back in service by May having any change, its usually crew problems or LIBAC delays, rather than mechanical)

Usually on that route, most of the business class is on upgrades, so them maintaining your cabin on a different flight should not be an issue. If you ask for a change, they may need bucket space, but if delays the day of force a change, they only need seats.

Personally, I would leave it, but day of, in MUC, contact the concierge for monitoring and assistance. They should be able to block off business seats for the later flights, and help you through YYZ if its at risk.

By May (we all hope), the I->D connection should be even faster than it is now. There will be customs, but no security. And by May, it won't require waiting for a bus, all walking. Or indoor golf cart riding, with concierge help.