What can I substitute for Cointreau
Cointreau is just one particular brand. You can substitute any other triple sec/orange liquor. Some may suit your tastes better than others, but there's really no reason to insist on the fanciest most well-known brands, especially since you're mixing it into cocktails. So sure, try the Meaghers, or anything else that looks promising. And when in doubt, just ask the folks at SAQ to help you out!