I will be traveling from Lagos to Toronto but via BA and Air Canada. LOS-LHR is via BA and LHR-YYZ will be via Air Canada, they are both on same booking and both bookings appear on their websites, however i will like to know if our luggage will be checked through to our final destination without having to pick and recheck in in LHR. Also, will BA issue us the boarding passes for LHR-YYZ on Air Canada?
If you have a single ticket and booking, then it is almost unthinkable that you wouldn't get your luggage checked through at Heathrow. Even though BA and Air Canada are in different alliances, that doesn't mean they won't cooperate on transferring baggage on joint itineraries.
Whether you will get boarding passes for both legs in Lagos is less certain, but if you don't, that's not a big problem. Follow the "flight connections" signs at Heathrow, and you will pass transfer desks where you can get the boarding bass issued before you need to show it for the transfer security check. Usually this is very quick -- most travelers these days already have their next boarding passes, so there is rarely even a line.