How do I get back the sales tax I paid in Canada? 
CANADA REVENUE AGENCY

 

How do I use Duty Free stores? 
DUTY FREE AT QUEENSTON
DUTY FREE AT LEWISTON
DUTY FREE AT RAINBOW CANADA
DUTY FREE AT RAINBOW USA

 

How do I get Nexus? 
Nexus

 

How can I get my toll refunded if I am a government official on government business?
Government Business Refund Instructions