Microsoft has shortlisted some of the Internet Telephony Service Providers (ITSPs) to be included into the Microsoft Response Point administrator application. These companies may not be available in your area. In which case you can setup another ITSP providing services in your area.
The Response Point system uses a standard SIP based trunk configuration which allows you to configure any ITSP providing you the SIP Trunk with login/password and the domain/ip address.
CIGear is also providing SIP Trunks for small businesses and VARs. Please check the number availability and pricing from the website http://www.33phone.com/ providing services across Canada.
A screenshot of the VoIP Account screen with sample configuration information is attached for reference:
