This is a comprised experience at best.
I have GV and have used a cellular iPad mini as (also) my "phone" (with buds) for more than a decade now. No problems and no sense of compromise. Yes, it's not Apple's default VOIP app but simply a
different VOIP app. There's
plenty of them in the App Store.
More importantly, Google Voice is not available in Canada.
Google Voice works just fine in Canada. I've used it there many times myself.
If you mean setting it up in Canada, the free version is not directly available but you can get it for a cheap monthly rate as part of a bundle of Google services there. Else, there must be many other VOIP services available in Canada. I encourage you to shop around and try some of them.
Secondly, most One Time Verification Code won’t work with VOIP numbers.
In my decade of experience, I've had this issue only 2 times... with neither being that big of a deal. For one of those, I used a backup VOIP app that I keep on the iPad and the verification worked with it. For the other, I verified with a friends number and have since been freely using the app for nearly 2 years now. Eventually, I'll probably need to verify again and I'll just use the same approach.
Secondly, my phone number has been used for more than 15 years, I don’t want change phone number and porting number to VOIP is PITA and it is also impossible to port number out.
My phone number started as a land line number in about Y2K, then ported to iPhone for a few days, so I could port it to a mobile number for a few days, so I could port it to a VOIP service... which eventually led to porting it
another VOIP service. Perhaps things are different in the USA, but an entity cannot keep anyone from porting their number to a different service. US carriers don't even has a say in that. You port and they find out you are done with them AFTER you are already with the other carrier.
I suggest you take a fresh look at VOIP apps, services, etc available to you in Canada. That's the path to getting your much "bigger" phone in the form of a cellular iPad. Else, you can hope that Apple will grow iPhones even more but that tends to happen a few millimeters at a time... so your wait will be long. Maybe Apple will roll out a "fold" at some point though very speculative rumors put that at many years from now.
Lastly, you can run VOIP apps on Mac too, effectively making maybe a 15" MBair into a "phone." I sometimes make and receive calls on my Desktop Mac and OFTEN text on it instead of phone or tablet screens. That may not be quite the "portable & light" you seek but if you carry around 2 of the bigger cell phones, I bet the relative weight would be similar... and all apps would probably be more enjoyable on that much bigger screen.
OR, you can have a Cellular iPad as soon as
today.