Any daffs sold in your area are hardy. And yes, mix them up. Keep in mind their final height and what they are being planted next to, so their leaves aren't covered from the sun while ripening. Leaves need to last till they turn brown to give food for next year's flowers.

I would not be inclined to mix them up :-) Personally, I like clusters of all the same bulbs together for maximum impact. Otherwise it is one bloom here, another there, and then wait a few weeks before the later flowering ones appear.

But it is really a matter of personal choice.

I wouldn't mix either. Imo daffodils look infinitely better planted in groups of the same cultivar.

Old House Gardens has a handy chart of heirloom daffodils that can be sorted by zone and season (early, mid, late):

https://oldhousegardens.com/display/?chart=Daffodil

Some of these are hard to find and the OHG is an excellent source, but others are readily available elsewhere too. Brent & Becky's, another excellent mail order nursery for bulbs, has a search function for different zones and the early/mid/late season is often included in a cultivar's description. I don't know if any of them ship to Canada but nonetheless can be used as a good information source for daffodils. There is also a comprehensive database at daffseek.org for finding suitable varieties. Hope this helps.

The earliest (for me) are February Gold. Then usually cyclaminus. Triandrus and Tazettas bring up the rear with the very latest being some of the jonquillas, Sundisc especially, but also Baby Moon...and the poeticus var. recurvus and Actaea. Typically, the season can run for 3 months in the UK.

I always use February Gold in my window boxes. They start flowering in late January most years. Just in time to get us through the post Christmas mood slump. So it can be 4 month plus season in my area.