To be clear: 1Mbps is the *maximum* specified bit rate for CAN. 125Kbps is a fairly standard CAN bit rate. I've also worked on CAN buses running at 2.4Mbps (clearly way out of spec, but also fully functional).
The CAN frame structure is not very efficient, so even at 1Mbps you will get nowhere near 1Mbps data through the bus. I believe I found (it has been a while since I ran the numbers) that you could get about 50% of that, due to the large CAN frame structure.