There once was many, now there are few, regulations that is. DND regs are inline with Treasury Board for the most part. You can find the POMV Mileage rates here:
http://www.tbs-sct.gc.ca/hr-rh/gtla-vgcl/index_e.asp
Appendix B is the "high rate" and below that is what TB refers to as "non-travel directive" which to us would be the "low rate". If memory serves me correct, the rate you are paid is normally based on the province in which the vehicle is "registered" and not the actual area you are travelling in, unless there are extraordinary circumstances. As far as distance is concerned, your OR will use the Canadian Distance Guide:
http://www.canadian-wellsite.com/Distance/Distance.htm
Need more info, check the CF Regs which will be CBI 209.25 or the CFTDI's. Happy reading!