When friends came to me for advice on variable vs fixed rate mortgages, my advice was always the same.  Take the variable mortgage but make additional payments to bring the total payments up to what the fixed rate payments would be.  Except in unusual circumstances (See Trudeau Sr.s term as PM), it is would be very unlikely that interest rates would increase by more than the spread on variable and fixed rate mortgages. 
For new mortgages where the variable option may not be available, assume a 2 percentage point increase at renewal and make payments as if the current mortgage was 2 percentage points higher.