Most of the Canadian champions (the big-winning ones) I've seen have had cropped ears; however they are also often shown in the US, which may have something to do with it. My 100% guess is that cropping probably does give the dog an advantage, but only because there are many US judges that judge in Canada, and they often can't seem to get past the crop. It should not make any difference since both are acceptable per the standard.
The Worldwide Boxer website is excellent for learning about the standard, and has pictures to illustrate the various points.
www.worldwideboxer.com
There are several other resources available for learning more about the Boxer standard - I am most familiar with the US so I'll mention those (and I think the only difference between the two is the ears anyway). The American Boxer Club has an Illustrated standard available, their site is
http://clubs.akc.org/abc//abc-home.htm . The Boxer Club of Canada should be able to point you in the direction of an Illustrated Canadian standard, their website is
www.showdogs.org/BCC . The ABC also has a new booklet, "Judging the Boxer" that is IMO better than the Illustrated - I'm not sure if those are available to the public yet, but you could contact the ABC and ask (specifically Stephanie Abraham, if her e-mail is listed, otherwise you could search for Trefoil Boxers and see if she's got a contact there.) I also recommend the Doberman Pinscher Illustrated, it goes into far more detail than any Boxer publication and the standard are nearly identical except for height and head. The Dobe Illustrated is available from the DPCA,
www.dpca.org The FCI Boxer standard is also helpful, the wording is different but the description is basically the same - Matthew has it available on his site,
www.marimat.com
Going to shows is always helpful, too, of course - but be sure that you take anything you hear about a dog with a grain of salt!
This site lists upcoming shows in Canada: