Some apps on iTunes is only available in the USA, they are made for USA market. Like Comcast app, its a USA company with USA region available only. You will not find this app on iTunes Canada regions, only iTunes USA region.
(Many American bank apps you cannot find on iTunes Canada)...
Resolve: You have to use the country version of iTunes for apps in that country to download the app.
How: If you want an iTunes app found in the USA version of iTunes then you must have a USA address and USA credit card in order for you to change your region on your iTunes account.
Just changing the region will not let you have access to that iTunes region. IE: to have iTunes Canada access you must have a Canadian address and Canadian credit card to access iTunes Canada.
Your iTunes ID and password remains the same, all you do is in your account profiles you change your address and credit card information to the country of your address and credit card, they must all be from the same country.
You can interchange from time to time between Canada and USA by changing your address and credit card for each country and update you apps that way and or obtain new apps from either country respectfully.
I do this all the time living in both USA and Canada.
BTW Comcast DOES NOT WORK IN CANADA even with the APP, its broadcasting is protected, only viewed in USA.