Note: 570 was actually imported and sold into Canada as a street-legal bike for a few years (around 2010-2012?). The 390 was NOT! Too bad - perfect displacement for Sask!
I used to live in Calgary, and the AB guys all do this - they plate non-legal bikes for the street. You can always find some license issuer that will give you a plate for it, and if they don't just go to the next one. Same applies here.
This does not make the bike legal to ride on the street! If you are in an accident SGI will not cover you.
Years ago there was a thread on a fully-legal way to get an RUM (restricted use motorcycle) plated in Saskatchewan. Check out:
viewtopic.php?f=2&t=671, and
viewtopic.php?f=2&t=1020. In particular, look at Shorty's post on what to do, and my post showing the inspection form on the 2nd thread listed here.
There are several hoops to jump through. The easy ones are adding signals and proper lighting and DOT tires and such. The harder ones include exhaust designed for the street and suspension designed for the street. The advantage is that if the 390 has the exact same suspension as the street-legal version of the 570 then you don't actually have to modify the suspension at all. KTMs are like this - the 300 XC-W has the same suspension components as the 500 EXC and 350 EXC, and therefore the dealer can confirm in the inspection form that the suspension components are valid for a street-legal bike.
If you do decide to try it, keep us all posted on how it goes. Lots of us would be interested. I would not suggest doing the "illegal" version - it could cause you a lot of problems.