Vianna,
We had a similar problem but found no problems or penalties.
We have a main site covering our main market in Italy in Italian and English, with a 301 redirect from the .it extension, and a one page frontpage with .co.uk covering the UK and slightly different wording from the main site, linking back to the English version of the main site.
We've never had any problems (touch wood), in fact it might actually have helped our click-throughs as we often see the main site ranked first (when searching in English) with the .co.uk site second and indented, making it stand out. The same goes for some other terms that are on both the Italian and English versions of the site.
SEs don't return results for the translations of keywords e.g. when you search for 'German course' you don't also get 'corso di tedesco' and 'Geschäftsdeutsch' returned in the same results.
As for the .ca and .co.uk question, I'd go for what I said above and change the text as much as possible, if only by modifying the keywords slightly (though both the .co.uk and main site domains are on the same server in Germany).
And finally, I really don't recomend using an automatic translator for site text, as anyone who has used a software translator to translate from one language to another and then back again can testify - the results are hilarious at best and downright ridiculous or disastrous at worst. Plugging blatantly....if you need some help with translations try out
Translation and language tools, and if you prefer to ask a professional translator to help you out, you can also request a quotation.
Good luck with the site,
Alex