Even a 5 pound trigger can get exciting on a bench until you learn to use it properly. Failing to follow through can cause doubling under recoil.
Smith Enterprise does sell a 4.5 lb trigger for a reasonable price. $125US. However, it'd require the U.S. export permit. Don't know and their site doesn't say, if they ship to Canada. If they do, it'll most likely require fitting to an M305.