"Am I in a weird microclimate or is global warming really catching up to us? "

The former, the earth actually has been cooling since 1998. According to NASA satellite data, It's political, not scientific. Currently co2 levels are the highest right now in my whole lifetime. Did we have a super warm spring?
Go by the plant rating, if your crape myrtle is facing temps beyond it's rated zone, string Christmas lights in it. They will keep it warm. I'm in zone 6A and many bamboo can thrive here. I have one planted outside. Also some Crape Myrtle are rated to zone 6.

Here is a link that might be useful: Crape myrtle in zone 6

Really shouldn't be difficult to find the Southern Magnolia at a specialty nursery in the Niagara region. Try Rice Road Greenhouses.

Don't bother with Little Gem, you want the hardiest possible M. grandiflora (Edith Bogue or Brackens Brown Beauty). It's close enough to the edge of their climate tolerance that none are going to get terribly big.

You'll want to plant it in a protected spot, sheltered from wind and (ideally) protected from afternoon winter sun (ie. northeast side of a building).

Welland may very well suit evergreen magnolias if you only looked a temperature tolerance. Unfortunately that is only one factor for broadleaf evergreens. Duration of sustained below freezing temperatures and frozen soil are much bigger factors as they impact the plant's ability to re-hydrate periodically during the winter. Welland is not nearly as friendly on that account as say, southern Ohio.