Ottawa has introduced "a new GPS fleet tracking system on OC Transpo buses to improve service". Even with such a system, there may be significant challenges to running buses precisely on time with variable traffic.
Once buses are GPS equipped, however, it is possible to provide estimates of when the next bus will actually come. Guelph, Ontario, and Thunder Bay, Ontario are already doing this, thanks to a company called Next Bus. Here is a live example, showing when the next bus will come to a particular stop in Guelph.
Inside and Outside Graphics are a live snapshot from NextBus.
There's an interesting service in Vancouver that allows you to text the bus stop number to '33333' and it will give you a list of the times the buses arrive at that stop. I use it all the time - it's exceptionally handy.
This has been in Edinburgh for a few years now. It's a good service but at busy bus stops can be a little hard to decipher.