She's on a terrorist watch listno, just kidding. Wouldn't it be awesome if she was?
People forget that Canada is behind US in film and televisionin fact, a lot of "American" shows and movies ARE filmed in Canada. (Look at her resume, right?) Canada gives Americans generous tax credits to use their people. You see a lot of American movie stars surrounded by Canadian actors in secondary roles. Legally, you have to hire Canadians. You also see Lindy Booth in everything, and Americans have no idea who Lindy Booth is. (I'm a long time fan of Lindy Booth.)
She can be a big fish in a small pond or girl #5 in an LA or NY casting call.

In interviews she talks about how she grew up in the Canadian film industry since her family worked in the business so she seems to have a loyalty to it. Plus she also comes off as a real private person so she might not want to deal with tabloids digging into her personal life with who's she's dating and all that nonsense.

Maybe she isn't motivated by success or money? May111cbe she is proud of being Canadian and enjoys supporting more Canadian Produced projects. Maybe she likes staying within the country to film, for all we know there is some reason stopping her from Working in America??
Perhaps she enjoys the more quiet success she has in Canada and would rather not become some over night super star high that's high in demand celebrity. Perhaps she feels compelled to stay within Canada and continue to have a successful career and life here rather than venture to America on the off chance she could be successful. Perhaps she feels that moving to
America would be selling out on Canada, sort of like Ellen Page. Love her to death but I don't feel she's really the epitome of Canadian, nor do I gather she really fits in with Americans either. She's like the odd duck.
I am pretty sure I once read that Katharine, Emily Perkins and Ryan Reynolds all went to the
Same acting sschool in Vancouver. And after she was in American Mary (filmed in Vancouver) I got the sense that she considers British Columbia/Vancouver home and would like to remain actively involved with the Acting community. Her family is probably all in British Columbia/maybe significant others if she has any.
I'm proud of her too be honest BC needs more home grown actresses like her.

I think that's her own choice. I believe she even said so herself in interviews.