If you are IFR in IMC and lose contact with ATC, you still have to fly somewhere. There are a set of logical rules that dictate the timing, route and altitude of that flight. I'd expect them to be the same in both countries, and they are almost word for word.
CFR 14, Part 91.185(c)(2) (USA)
Altitude. At the highest of the following altitudes or flight levels for the route segment being flown:
The altitude or flight level assigned in the last ATC clearance received;
The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in § 91.121(c)) for IFR operations; or
The altitude or flight level ATC has advised may be expected in a further clearance.
AIM 184.108.40.206 (b) (Canada)
Altitude: At the highest of the following altitudes or FLs for the route segment being flown: the altitude(s) or FLs assigned in the last ATC clearance received and acknowledged;
the minimum IFR altitude (see RAC 8.6.1); or
the altitude or FL ATC has advised may be expected in a further clearance. (The pilot shall commence climb to this altitude/FL at the time or point specified by ATC to expect further clearance/ altitude change.)
Curiously, while routing defaults to the flight plan, the flight planned altitude isn't mentioned in here, unless the last clearance received was the IFR readback including the flight planned altitude. So that means that if you're departing somewhere and really don't want to fly at the MEA to destination, you'd better get the controller to say "expect flight level 230" and not just "expect higher."