Thank you financially, criminal or medically it should not be an issue.
I never applied for polish citizenship for our son as he was born in UK and we don't plan to move to Poland, it's not brexit that is making us move it's more of a dream to live in Canada.
Lets believe, that just like for Japanese car manufacturers, Brexit has nothing to do with your decision.
Ok as long as you are OK with following, no problem:
1. You will be most likely worse off than in UK (also this is a bit debatable depending how will UK look in few years), but unless you or your husband are very specific professions, you will be worse off.
2. If your spouse was borne outside Canada and he has obtained his citizenship by descends, your son does not have right for Canadian citizenship (second generation abroad). From what you have told so far, it looks that way
3. If you decide for inland spousal sponsorship, you will have to come to Canada with your son and live there until your spousal sponsorship. Be aware that as a visitor you have no right to enter Canada. So technically either your ETA request can be denied or your can be denied on borders. Also this is not very probable, but still possible. In that case you will have to use outland spousal sponsorship and live abroad (UK or Poland) until decision is made.
4. You can get work permit for the time of inland sponsorship. However it takes around 3-4 months to get it after you will apply for it. But while you will be just a visitor you have no right for Canadian health insurance. Be ready for that.
5. Be aware that Canadian health insurance system is worse than one in Poland and most likely worse than in UK. (for example unless you have additional health insurance given by your employer or a private health insurance, you have to pay everything by dentist, optometrist, chiropod - one dealing with legs problems).
6. your diploma from studies from Poland, will be most of the cases worth almost nothing (it depends on your profession, but most of the time you have to redo certain exams and additional certification).
7. Similar will go for your husband (also he has higher chances for something to be recognized).
8. Your husband, despite being Canadian, will be treated as a newcomer when it comes to getting first job (simply because for some magical reason foreign work experience is worth much less).
9. Prepare that from certain age you will have to pay for education for your child (from app 16-17 years old and even sooner if it will be a private school). Compared to almost free European universities, education can really get expensive.
10. If you are looking forward to a better house market, well not really. If it will be cheaper, then it will be far away from any decent job opportunity. If it will be close to a job opportunities (except of some professions), then it will be in par or maybe more expensive when compare to the local salary situation.
11. Food price will be comparable to higher, but with a generally lower quality when compared to EU regulations.
12. Internet and phone call prices will be over the roof.
13. Gas prices on the other hand will be a bit cheaper.
14. Public transport is comparable to the public transport in EU cities of app. 1/5 to 1/10 size (for example GTA area that has decent public transport network, would equal with it Public transport level in Prague (total quantity); however GTA has app. 4-5 millions, while Prague has only around 1 million.
15. Flight tickets are expensive (again compared to options in EU).
16. Yes people are friendlier and nicer (at least on the surface). But at the end of the day they do not really care (so more or less same as in any bigger city in EU).
17. Nature can be nice, as long as you agree to live far away from any bigger city.
So in a nutshell it depends what you seek.