C20LET is total unobtanium in Canada, since they never marketed on this side of the ocean. Same with C20XE...
Also, C20LET were not even that common in Europe, so expect to pay big bucks to find one big bucks the freight it here, and heachaches to find the parts to keep it alive.
The 8V turbo (C20GET?) was sold here and can be found for peanuts and with even mild tuning, will be more engine than you can ever wish for in this chassis, which wasn't the best, even when brand new in an Opel dealership...
Also, there is more to the euro engines than just the head. The bottom end was suitably equipped to deal with 150hp (XE) and 200hp (LET), so a 20 year old granny engine build to deal 100hp on a good day may not be able to cope for very long...
If you are thinking of using the Optra head, you might as well use the whole engine... If it fits, which I'm not sure it will (I haven't kept current in this matter). Also, there is an "ecotec" used in some Daewoo Nubiras that could be used. It has nothing in common with the common Ecotec still used in GM cars, but it too can be had for peanuts - if you can find one...