Other Canadian area codes

That's how Cell phone business works. It allocates local area code according to your current address.

Saskatchewan is not part of Fizz subscription area. Therefore it's impossible to have Saskatchewan are code with Fizz at the moment. Fizz might decide to expand their subscription area to other locations in the future ( long term ).

Hi Kevin, my wife and I were in a similar boat after moving to Quebec and wanting to get the better Québec cell phone plan prices but keep the Ontario numbers we've had forever. Bell flat out refused for her, which is who she was with at the time, and Koodo tried but had troubles because the system wouldn't let them port her phone number and set up the new account on a Québec plan. The only solution was to get a Quebec number and then later port in her Ontario number in the online account settings, which also switched her account over to Ontario again so although she didn't have to change her plan she's no longer able to get Québec plan options if she wants to change again. When I switched to Koodo as well about a month later I had to do the same thing, with the same result. Not the same problem you're experiencing, but similar and due to the same cause - cell phone plans are still very much tied to area codes for everyone right now. Even though it makes no sense anymore and hasn't for quite a few years.
When I switched to Fizz a few months ago I also was unable to port my phone number because of the area code restrictions. So what I did, and I recommend you do if you are staying in Ottawa permanently, is port my number to Fongo instead for $25 and installed their app on my phone. With the cheap LTE data offerings from Fizz you can still do all your calling within Canada through Fongo and keep your number if you want, or you can forward all calls to your new Ottawa number and nobody will be the wiser. And you can still receive text messages on your old number too, then reply to them from the new number and ask people to update their contact card with the new number. It's about as seamless as you can get for a truly region free number at no extra monthly cost. If you still want to be able to reply to texts from the old number you'll have to pay Fongo a small monthly fee, I think $3-4. Note that (just like Fizz right now) Fongo doesn't support most 2FA texts at the moment. You can do something similar with other voip services, like voip.ms, but from what I've found the other options all have monthly fees attached.

Get a Fongo account, and port your number to there. Then call forwarding all number to your new ottawa number. This way you won't miss anything from your old buddies.