The only company which has no cap that I have found, is Lewis & Lewis (there may be others since I checked). We now recommend everyone use them for their insurance or at least check this out on the policy they intend to buy.
We also use and recommend Lewis & Lewis but there are a couple of points travelers should be aware of. Lewis & Lewis is a US company that sells Mexican insurance. There are a number of Mexican insurance companies and brokers in the US such as L&L which all sell insurance from the same companies - the same policies for about the same amount. We feel with L&L we can get help on a personal level if we ever need it in Mexico - help the other companies may not provide. This is a personal impression which is not based on personal experience - other companies may be just as good. We will only find out should a need arise - which we hope never happens. We recommend L&L based on what others on this forum have said about them over the years.
Also Note - It is our understanding that Mexico has limits on how much liability someone can be sued for - unlike the US where people sue for as many millions as they can get. More questions to be asked.
Also about insurance - some US policies and companies do cover comprehensive - collision etc. (I don't know about Canada) but only Mexican companies can provide liability so you must buy liability from a Mexican company. If you do not buy liability and are in an accident the law in Mexico is the police arrest you until the whole thing is sorted out (could this take months?) - with insurance the insurance takes care of this and you will not be detained. You should check with your US or Canadian insurance to see if you are covered for collision etc. We changed to Progressive in the US because they cover us for collision in Mexico - not all companies do. Having US collision means we can get repairs in the US at US rates - but questioning Progressive told us they will only pay for so many miles or so many dollars toward towing back to the US - I forget - or maybe it is our Good Sam policy that limits - more questions need to be asked of your insurer. But Progressive only covers our motorhome and not our towed vehicle so we buy Mexican insurance for the car. There are many questions about insurance we cannot answer because it is just to complicated. We read of people buying something called "driver's license" insurance which is supposed to cover you no matter what vehicle you drive - we have heard good and bad about this and have chosen not to risk it.