The thing is, they inspect the plumbing and everything to make sure its up to code.. if everythings is up to code, then it shouldn't be an issue getting it legalized.
The only things to make sure would be:
-Seperate entrance
-Bedroom has a big enough window for emergency exit (dependant on percentage compared to size of occupancy)
-Smoke detectors (2 IIRC)
-6' 6" headroom in 60% of the suite and at all exits/entrances
Assuming it's in Vancouver:
Licences & Inspections, By-law Administration and Records Services, Secondary Suites Program