Would it be a silly idea to leave my permanent job and go back to student status at this age ?
Nope. Lots of guys and gals at my outfit are starting a second career in aviation well into their 50's, which means they were students in their 40's. Starting at 38 will likely put you out of the running to ever see heavy jet command time in Canada as there will be so many younger people more senior than you at the airlines, but as long as you're comfortable with that, you're fine.
Is [C]anada a good country to continue my CPL ?
Yes. There are a lot of good schools to continue your CPL. Like the US, you have to decide what type of climate you're willing to live in before coming north as not all of Canada is covered in igloos. Vancouver Island is beautiful this time of year. Winnipeg; not so much.
However, what you do after you earn your CPL is a whole other story. I would generally suggest that American pilots stay south of the border as the earning potential is much greater. I found starting at the airlines in a similar position to you here in Canada - late 30's with an ankle biter - was very difficult. I had the advantage of already having buckets of total and command time and the airline desperately needed experienced Captains, so I obtained a very quick upgrade. However, coming up on 4 years later I am only now emerging from the debt caused by those 6 months I spent in the right seat as a single-income family. Had I not known the upgrade was quick, I would not have come to the airlines. With a fresh CPL, you can expect at least 2 to 3 years right seat at a regional, assuming all plays out well with the economies of the world.
If you're going to do this, do this with eyes wide open. It is a great gig and I wouldn't want to do anything else, but it is going to be akin to white water rafting for a while. Hunker down, don't get extravagant and you'll do OK. It'll be just like you're an apprentice again!