Yes. If you ignore the letter the first time, they will reschedule you after 3 months (from experience, it's 1 month). There's no effect for the first time, but you will have to explain for the second or third time.
*** Wow, please NEVER "ignore" any notice from government, particularlly from Immigration & Citizenship of Canada. Instead, please follow the instructions from the notice or contact relevant parties for other arrangements.
