Is it true?

That BMW will stand by there engines to start in conditions to -40?? I have a 2003 X5 and
since recently just moving to Canada i am unsure if i need to install a block heater.

Your '03 is long past warranty, and I don't recall any written vow that any of their cars will start in -40 degs...a car is a car, regardless of brand or current tech.

Cold weather starts are a function of oil viz, battery condition, engine condition, etc. Our '01 has started a few times, no prob, in -10 F, but I wouldn't want to have to do it for a living during the winter season. You might do some web noodling on block heaters, very cold weather condition starting, Great White North anecdotes, etc.
GL, mD

+1 on the above. Plus silicone heater pad/wrap for the battery.