From the NBCC:
Maximum ramp slopes for non barrier-free paths of travel:
1:10 for exterior ramps and interior ramps service residential occupancies
1:6 for mercantile or industrial
1:8 for all others
If ramp slope exceeds 1:12, maximum rise of a ramp shall be 5'-0" (1500mm)
For barrier-free paths of travel:
1:12 for maximum distances of 30 ft(9m), for ramp lengths in excess of 30ft, landings must be provided at maximum 30ft runs.
They however recommend 1:20 and caution using steeper than 1:16 as they can be unsafe to descend in cold climates (exterior ramps).