Hi fruswlo,
This is assuming you are thinking of doing a Master's (or PHD) and not a Bachelor's.
If you have not done so, you should ask your potential professor/supervisor about grants and monetary support. If he has external funding for his project/your potential research, then he may be willing to pay for experienced help like yours. University profs are always in need of students to do work for them, just whether there are students willing to do it for cheap or free... Note that students with good academic record can get government bursaries and grants, though I'm not sure how it works with international students. Student salaries and bursaries are not taxed.
In terms of vibrancy of student life, there should be no worries. Montreal downtown is occupied by 3 university campuses -2 of them English. The entire downtown retail sector is in close proximity. Concordia also sports a large Asian demographic -though mostly Chinese.
In terms of financials and whether you can find a part-time job for you to be comfortable, I'm not sure. Most students (during their bachelor's) do retail or restaurant work part-time to support themselves. To work in retail, in restaurant, anything related to customer service, French is required 99% of the time. Some may have a specialized part-time job, but it's more rare. Software is booming, there are
surely small start-up businesses who would welcome an experienced software guy part-time, but I'm not sure how to best find those. Once you're a Concordia student, you'll have access to paid internship and job postings from their website.
Once you graduate, finding a job shouldn't be hard. Software is big in Quebec (government investment and subsidies) and is getting bigger in everywhere. In Montreal alone, practically every major game developer has a presence, there's Nuance, there are many special effects companies. 2-3 years ago, a software grad could pick and choose job offers -and that was with 4 universities pumping out engineers. Beyond the border in the United States, there are even more opportunities for experience. A company like Amazon in Seattle is always hungry for talent and experience.
Also software is an predominantly English industry. Nobody codes or searches for help online in French. Your prospects for a job would be better if you were French-fluent, but the state of the industry is such that there are enough positions if you weren't. Apply for positions that state Bilingual requirement even if you don't speak French. The language requirement is sometimes required by law and may not actually reflect reality within the company. Job postings requirements are idealized scenarios listed by the hiring manager anyways.
To get an idea of how much a flat would cost to rent, visit
Kijiji: Free Classifieds in Canada. Find a job, buy a car, find a house or apartment, furniture, appliances and more!. It's the most popular classifieds in Canada. Note that if you do not have a Canada IP address, you are enable to email through their interface. You can only call (if the ad gives telephone numbers). Use google maps, look at anything walking distance to a metro (subway) station. Areas around McGill university (the McGill ghetto ;-) ) could also be of interest.
Canada is very different from Japan though. We're not as orderly and courteous, but it's more relaxed and at the same time, you're never bored living here ;-) hehe.
Good luck!