I got this extract from ROP twice. Just go to the ROP Driving License Office at Azaiba (Near Golden Tulip) and say you are moving to Canada, they will know what you are looking for.
They will ask you for air-ticket to Canada along with your Original License, but the first time I got the driving license extract, I didnt have a ticket and upon explaining that I was going to be moving to India first and then go to Canada, they accepted and gave me the extract. Still having a ticket helps.
There is no charge for the Driving License extract.
The extract is in Arabic and will need to be translated by a certified translator in Canada. Canadian Consulate in Oman might also be able to do but I havent explored that option. Dont get it done from regular translator in Oman, that wont help.
The extract will be dated and valid for 6 months from date of issue (hence I had to obtain a second copy) and your Oman Driving License will have to be valid as well when you apply for Driving License in Canada.