So the factory warranty on my 2008 M3 expired this month and I figured it would be good to get an extended warranty since I will likely keep the car for at least a few more years (been a great reliable fun car). Figured my research may help others...
BMW has their own extended warranty for M3's but it is only available on 2011 and newer cars, hence not an option for my 2008. Most of the BMW dealers seem to recommend Coverage One Ultimate so I decided to go with that. I had Coverage One before on an older BMW and found that most stuff that broke was covered, and usually the BMW dealers are helpful getting things approved as they of course want the work.
Next I found out that Coverage sells a "new" car warranty which extends your manufacturer's warranty by 3-4 years and also extends the mileage to say 120,000km in total. Optionally you can buy a "used" car warranty which doesn't extend but rather gives you 3 or 4 years and a certain number of kilometers. Apparently the coverage is otherwise identical as it is the same "Ultimate" plan. Interesting part is that the "used" warranty is actually a lot cheaper by $500 or more.. so I ended up going that route simply because of the price advantage.
Once I knew what I wanted to buy, I checked with several dealers. First dealer I went to was Budd's BMW in Oakville because that is where I bought my car. They quoted me $4,180 for a 48 month "used" warranty with 48,000km and a $200 deductible. After a bit of negotiating they offered me the warranty for $3,900. I then called two other dealers, Endras BMW and BMW Autohaus. Both of them quoted me $3,280 for the same warranty! I checked with Budd's if they could match but they were not willing. So I purchased the warranty at Endras, mainly because that is where I have done most of my service lately and they (as did Budd's) were therefore able to waive any requirements for a physical inspection of the car (which would cost me several hundred). BMW Autohaus needed to see the car, hence they were out.
So the lesson here is, shop around because there is huge markup on these warranties and some dealers are much more eager to get your business than others.