As you mentioned in your question the the website is meant for an international audience. SEO ranking aside the international audience will be much more used to the .com domain than the .ca TLD.
COM vs CA
As of today the TLD does not matter much as long as you are not using free TLDs that are often associated with scams (suck as .tk for example). In fact Google has explicitly mentioned that the TLD is often ignored and making a website about a museum using the .museum domain (yes it exists http://about.museum/) will not help you at all.
Search engines are actively trying to incorporate localization - the Russian search engine Yandex for example offers different results depending on the neighbourhood of the user. With this in mind it is important to decide whether local Canadians or the international audience is your primary target in order to future-proof your website.
Link Building & Promotion of a 301 Redirect
Another important question which you asked is whether it matters which website you promote (co or com). Technically there is almost no difference when it comes to the power of the accumulated links (which boost your search ranking), however you must have in mind that this could change any day.
Currently many black-hat SEOs link to short domain redirects and point these links to the websites that they want to rank. Google will inevitably find a way to penalize them, so I advice promoting the main website not the redirect.
Permanent (301) vs Temporary Redirect (302)
Additionally make sure to use a 301 redirect not a 302 or javascript redirect as they are completely different in the eyes of search engines.