Google.ca results significantly different than other Google domains

I was hoping someone could shed some light on an unusual situation I have. I've got a website with a domain for one of my products, it looks like this:
www,product-name,com

When I search for "product name" on Google.com, Google.co.uk and Google.com.au it comes up at #1...for Google.ca it comes up at #238. Has anyone else out there seen this phenomenon before?

Any ideas what would be causing this? It's been like this for a couple of months. I am concerned that this site is on its way to becoming deindexed (about a year ago I got the "unnatural link" message from Google), but it's been stable in the on the other Google properties, so I don't want to knee-jerk on the issue.

Thoughts, ideas?

It's not a "phenomenon". Google uses a lot of complicated algorithms to deliver what it thinks are the best results to the users. In this case, on google ca, they don't think it's number one. I've also seen one person google something, it show up on page 10, another person google the same thing, and it show up on page one. (on the same google site).

I'd be fortunate it's number one for those three sites.