I have flown through YYZ T1 many times and know it better than I care to admit, but have never, ever been to T3, so I´d appreciate your input:

1) What would be the process of connecting from T1 (arriving on AC from EWR) connecting to T3 (AA to ORD)? (Yes, I know the routing is ridiculous, but just ignore that for the moment.) I guess clear Canadian immigration/customs -> go landside and take train to T3 -> go through security and US pre-clearance? Any short-cut to this?

2) How much time would you recommend for such a connection? (´ll be travelling with hand baggage only, flying on two separate tickets and can access priority check-in/security where available - but don´t have NEXUS/GE)
I´m thinking 2h + 1h buffer in case of a delay ex-EWR = 3h.

Thanks!