It's quite hard to give general advice about zone-pushing (or zone denial) without more specifics about your location. Where are you and how long is your growing season? Are you in an exposed location?

Very generally, it seems that you're pretty marginal for all of your listed species. Flowering dogwood survives as far north as Ottawa (zone 5-ish), but it's very likely that low temps will kill off most or all of the bracts (no showy 'flowers'). Redbud is equally iffy.

There are, however, a number of lovely flowering trees that will survive (and maybe thrive) in zone 4. Black locust is really underplanted, and it puts on an amazing display every June. American linden (and many of its hybrids) has an amazing fragrance, and is well worth a look. And, while I'm never a fan of invasive foreigners, I have to admit that I love the smell of Amur maple when in flower.