It's so cool to find another person from Ontario on here! I felt the exact same way when I found out about how awesome they are on Youtube many years ago. I feel your pain trying to find a critter nation cage. They're sold out a lot whenever I check, since they are pretty much the best cages. Do you have rats yet, I can't really tell (I sometimes miss stuff if it's not overwhelmingly obvious lol) but I can't wait until you can show pictures of them regardless! I hope any rats you may or may not currently have (or your future rat children) do great and behave at least most of the time lol.
I still consider myself a newer rat owner, so I'm not sure how good my advice is. But for starters I'd recommend you fill their cage up as much as possible since my boys had some issues because of boredom. Which is fixed now! You don't have to break the bank either, I found that my boys love those small baskets from the dollar store and when they were smaller would sleep together in one. It was so adorable. Don't be afraid to zip tie things to the cage bars, I'm pretty sure most rats won't bother chewing them and it give you a lot more freedom to add things. Their favourite thing I bought that's actually for pets is probably their Space Pod/ Sputnik. Now that they're bigger and can reach it from the bars they've made it their nest and they all sleep together. If you can find someplace near you that sells them I 100% recommend. I do fill anything made of plastic with these soft pet blankets that I get from the dollar store, just so they have something soft to lay on. Trust me, there is nothing cuter than moving a blanket and finding 3 baby rats cuddled up underneath it.
This got a lot more rambly than I though, oops. I hope you get some good advice on here, everybody's been really nice to me so far!