Licensed OAA architect here.  

(OAA stands for Ontario Association of Architects)

I can't speak much about the UK vs Canadian license process but I can provide some info as to the Canadian working world.  To you points:

• Typically, fresh grads in Canada are considered intern architects if they are registered through their provincial associations and are in the process of completing their minium exp hours.  These are junior positions and assumes the applicant has an accredited M.Arch (or equivalent ie B.Arch or BAS).  B.Arch degrees do not exist in Canada anymore.  Those with related arch bachelors or college technical backgrounds but no M.arch get grouped into the arch technologist or designer category.  Normally all 3 of these groups are considered equally junior.
• Previous experience is always a good thing but there is no specific requirement for junior position.  Keep in mind that architecture education in Canada has evolved and distanced itself from the American system and I've found that many employers expect fresh grads to be able to reasonably handle CD sets and construction details from day one (ie. without major handholding).  
• In a large city like Toronto, you will face competition from at least the 3 arch schools in the region (UofT, Ryerson, Waterloo) plus all those relocating from other places in Canada and the US.  Loads of internationals land in Toronto because it is the largest city and there is no need to learn french.  
• Jobs are plentyfull in Ontario and there is tons of construction happening.  The problem is that there is a big shortage are skill in the project architect & project management roles (8-10 year exp range) but no shortage of fresh grads.

Aside from that, we use the metric system because it's better and have our own endless circle of codes.

I went the opposite direction (Ontario > UK).

I would recommend having contacts in place before moving. While nowhere near London levels, Toronto isn't exactly a cheap place to live. It would be difficult to have an extended stay without a job. Canada also doesn't really use recruiters like in the UK, so I would not expect to have that as a fall-back.

For terminology sake, as a fresh Part II finisher you'd be the equivalent of having an M.Arch in Candada/US. You are eligible to pursue licensure (our Part III equivalent), but haven't finished that yet. You're considered an intern architect, albeit in a professional sense (ie, not a coffee-fetcher).

Some of the bigger firms, particularly ones that pursue international work or have partner offices in other countries, should be your primary target. They will appreciate the international outlook that you can bring, cross-pollination, etc.

Its a good market in most of Canada right now - and I think any place you can weather out the Brexit storm is a good call. You should look at visa options before going though, is there a YMS available to you? If so, how long and what are the restrictions ?

Yeah I need to look into visa's further. I'm not looking for sponsorship, just to enter on a work permit, which is what was suggested would be possible when I filled in the free assessment based on my experience/education.

Check out Hays, Randstad, Michael Page and Design Group staffing. It is my experience that they heavily use recruiters in Canada. As for places (cities) to work in: look at Toronto, Vancouver, Calgary and Edmonton in that order. Edmonton and Calgary will appreciate your international experience the most and because of that will be easier to rise faster within. In Toronto and Vancouver, development is booming but you will not stand out as much there as you would in the other two cities. 

I agree that trying to land a job outside of the country seems to be the most safe, so does moving to Toronto where you have family. Utilize LinkedIn, reach out to people who work at the companie that you want to work for who have some sort of commonality to you, like they are an international from an outside country who relocated to Canada and then try to get them to agree to have a phone conversation with you. Do not ask for a job directly buy just ask for an informational interview and that you want to learn about their path and background. If they like you, they will try to help you.

Best of luck!

also expect to donate half of your pay check to the liberal agenda in Canada. Remember Canada had zero debt until Pierre Trudeau took office with all his socialist programs.... and now his son is leading us further down the hole. 

...call it what you will... but your buddy Justin is on track to setting a record for increasing federal debt... and that’s a fact jack! His father never in his 17 years of being prime minister balanced the federal budget. That’s also a fact.  So you can attack all you want but numbers do not lie. As far as taxes... see gas tax, milk tax (raising of minimum wage), property tax, 13% hst on everything you buy... yes it doesn’t get out of your pay check directly but the government gets it elsewhere. So hit me again with your training wheel comment cause I’ve been around the block for awhile.