Heya - und liebe Gruesse an die Stadt meines Herzens :) Wien ist super!
I'll swap back to English as we are here on an English speaking board, but can PM in German, too if that is easier :)
A lot of 'Wrangler Stations', i. e. barns and farms in Canada make their money by guiding tourists around trails. Most of their wranglers actually are volunteers and very few offer paid jobs. But - especially if you like to further your career on it, and go to college or similar, they value such 'volunteer jobs' in the CV quite highly.
First thing: Google for National Parks in Canada (Jasper, Banff, Waterton, etc.) then find activities there (Horseback riding) - normally the barns have their own webpages and then it's just a matter of emailing them and writing to them.
Make sure you also speak to the Embassy about what visa will be needed to do this. I joined the Volunteers in Park program at the Great Smoky Mountains National Park last year and despite having everything cleared with the Embassy of USA and the National Park, actually getting into the USA through the immigration officers at the borders turned out to be a pain :( ... I have no idea about the procedures for Canada, but could write a book about the USA - and it would not be pretty...
Also: If immigration proves to be very complicated and as strugglesome as it was with me last year, checking into Ireland and England might prove useful - advantage: You don't have to bother about visa issues at all (the only useful feature of the EU :P ) ...
A couple of helpful search tips:
Website for National Parks in Canada: List of National Parks of Canada - Wikipedia, the free encyclopedia
(also contact the Canadian National Park Services for their potential programs. I know the USA National Parks sometimes offer internships to work with their mounted Back-Country teams, maybe the Canadian ones have a similar program?)
I think, this is their official website: Parks Canada - National Parks of Canada - National Parks of Canada
As soon as you google for the national parks, and add horse back riding, you will get tons of lists of websites of riding barns that offer those services :)
Alternatively: Horsejobs.ca - Welcome Horsejobs Guest!
Good Luck :)
I know, it's a pipe dream until it comes true! I was so excited when I heard from several National Parks and got accepted into a few and then the actual preparing, visa work, etc. began ... Fun times ! :)
Let me know if I can help with more info !
PS: I almost would have gone and did their work student program here: http://www.ewsz.com/workingstudents.asp
A swiss family in Canada - before I was able to actually fly, I had a major car accident :( and there went my dream for joining them :(