Hi Cyril.
Google released a webmaster blog post that covers this specific instance quite extensively:
http://googlewebmastercentral.blogspot.co.uk/2010/03/working-with-multi-regional-websites.html
But in summary; yes if the content is going to be largely the same then I'd suggest using the canonical tag to identify the .com as the original source. The advantage of this is you wont fall into any duplication issues within Googles algorithm, the disadvantage being that the sites containing the canonical tag may struggle to build up their own authority as you are essentially telling Google that the content is not their own, so some of the link juice should be credited elsewhere.
Have a read of the webmaster article, they go into a lot of detail about the issue which will hopefully guide your path.
Good luck.
David


