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!

You can, generally, substitute another brand Triple Sec for that, since that is what Cointreau is. If you're used to Cointreau, you might want to transition to brands known for being of decent quality, vs. bargain basement (like, say Mr Boston), so the adjustment isn't too much of a shock.

Keep in mind that Grand Marnier, while an orange liqueur, is actually a "curacao," not a triple sec (Cointreau is a triple sec, AND a curacao). Triple secs have a neutral spirit as their base, while Grand Marnier is brandy-based. I think all triple secs are curacaos, but not all curacaos are triple sec.

Article comparing brands of Triple Sec, with prices and links to reviews

Cointreau is a "curacao" or orange liqueur, and more specifically it is a top-shelf brand of triple sec. Any other triple sec, as will other curacaos and orange liqueurs such as Grand Marnier, GranGala, Combier, various Blue Curacaos, etc, will get you a similar result, possibly with color and minor flavor changes.

Some things have substitutes that are acceptable, depending on use. The only real way to know is to try. In some cases the substitutes will turn out not to be suitable (varies with taste, opinions, etc. - not something you can really depend on anything but your own experiments to know for sure.) I find a particular low-end-brand of creme de cassis to be superior for my purposes/tastes to several supposedly higher end (and certainly higher priced) versions I have tried occasionally. For other things the definitive brand is well worth it (and was even when I was in college/on a tight budget), at the rate I drink, anyway, and clearly superior in taste (to my taste.)

Some liqueurs can be be effectively knocked off with vodka/grain alcohol, sugar, and flavorings/fruit, (often +time) if you are on a budget and like projects. I did a pretty satisfying plum "wine" (as it's typically called) that way, but it took about a year to do, which might be beyond your planning horizon as a college student. Things that don't involve steeping actual fruit can be much faster, but might not save much money, depending on the cost of the flavoring(s).

At least of the bottles I have had in stock, Cointreau and triple sec are rather different, though both are orange-flavored, with the Cointreau being 40% ABV while the triple-sec was either 15 or 7.5%. Your linked version is 35%, so that obviously varies. Quality of the fruit flavor and lack of off flavors will matter more than the precise alcohol content, generally.

You could substitute Bols Curacao Triple Sec which has an ABV of 38%, close enough to that of Cointreau. If that isn't available in Quebec, Meaghers Triple Sec with an ABV of 35% certainly is.

You can substitute Patron's Citronge, or Combier orange liquor. Both are about $26 here in the Bethlehem, PA, which is about $10 cheaper than Cointreau. I have used both in Winter White Cosmos and regular Cosmos and each works well. And each actually DOES taste like Contreau.

I use the Cointreau in my margaritas, which I make with fresh limes and a quality tequila. (Cazadores reposado is my first choice). I have not found a suitable substitute. Gran Marnier is different: it isn't clear and has a very different taste. Not acceptable to me. I also tried Patron orange liquer. Didn't like it. Pretty sure I would not like the triple secs mentioned here.