You can renew a passport at any time. Any unexpired time on your existing passport will be added on to the validity of the new passport, subject to a maximum of 9 months . So, if your passport is renewed now (9 months before your existing passport expires), your new passport will be valid for 10 years and 9 months:
http://www.ips.gov.uk/passport/apply-renewing- when.asp
If you're emigrating to Canada, I assume that you've already checked that you can meet the family or professional requirements for admission but, if you need further information, it can be found here:
http://www.cic.gc.ca/english/immigrate/index.a sp
Chris