Question 1) Ans : You should try to use Proxy server to check rankings from Google.com *( US). Google can display different rankings when Google.com is accessed from New York and Texas. Therefore make sure you are using the right mode.
Another option is to use specific I.P addresses. For example Google New York can be accessed as
Google 
Similarly you can try using proxy or specific I.P addresses.
Question 2) Ans : If your canadian clients host their site in Canada then they will gain preference in Google.ca.
Along with this they will gain rankings on Yahoo + Msn.ca. This could bring more traffic from these search engines as well.
However if your Canadian clients have their website already hosted in U.S then it wont be much beneficial to suggest a hosting change. This could be a mammoth activity if website is a large e-commerce store.
You can try setting the geo target location for your website within Google account. Read more about Google geographic targeting at
Google Geographic Targeting
I am sure it will help you
