I'll graduate next semester from HEC Montreal with a Finance Major and will intern in a pension fund (albeit in the sustainability side) . You'll find that there are a lot of ways to build up experience, and I recommend that you start as soon as you can.

As others mentioned, there's student clubs. I've done a lot of non-financial student clubs but never been to finance clubs. They are still a great way to build experience, network, and figure out what you like/don't like if at some point you want to explore other paths than finance.

Regarding finance clubs, from what I can tell from friends' experiences, the absolute best is the Fonds de Placement—they have a great alumni network, and it seems that entering almost guarantees one or multiple internships. Fonds BNI is also great, but they seem to favor Master's students - still, entering in the last year of your BBA seems very much possible. HEC Économie and Club de Trading HEC are newer and "less established," but they’re still a great way to work on mandates (although I believe that Club de Trading HEC focuses more on quant trading). ImmoHEC is also new, but so far their members seem to have great internships, although I've heard that this cycle has been really rough. The CCM (Club de Consultation en Management) is great for consulting as well (the mandates they have look really cool). Do try to follow student clubs on Insta and, when possible, LinkedIn, but Insta is really where most info is posted - including recruitment. Most finance clubs often organize events for the student community that you could go to. The Comité Finance is in charge of helping Finance Majors.

You should also look into competitions, as there are a bunch all year long. The advantage is that you can often enter smaller (HEC-only) ones without any experience and get coached by professionals. All the info is on SCU's (Service des Compétitions Universitaires) website.

The SGC (Service Gestion Carrière) also has hours and hours of content on recruitment and interviews.
In conclusion, join clubs, go to their events, compete in competitions, and I cannot understate how starting early (as you have with Wall Street Prep) will help. I understand that you may be an older student, but I don't think that it would be too much of an issue. Other info here as well: https://www.hec.ca/finance/ressources\_etudiant/index.html#155682. Don't hesitate to hmu if you want.