Need M0/M3/M4 supplier recommendation, CAN Bus

So, I'm just now migrating to ARM from PIC. I hate most things about Microchip's implementation of CAN, but I do love the ruggedness of those chips. Since I do far more work on CAN than analog I'm confident that Cortex is what I'm looking for.

However... Of the major suppliers NXP, Ti, Freescale, STM, SiliconLabs, etc, I'm not sure who to go with.

1. Does it matter? I'm pretty sure I'll be using Keil, so is there any signifigcant different between X and Y brand Cortex chip?

2. I work in automotive. Basically, the only requirements I have in a brand of ARM is that I need a small cheap on with 1 can controller and a USB device (host ideal). As well as a "big" chip that has two can bus ports and 1 USB host/device. That's it really. I think STM is winning so far. Ti doesn't have a range of M0/+. Freescale seems expensive and limited for dual CAN. NXP looks good but limited in selection at least compared to STM32Fxx series. Anything else I should look at?

3. If anyone else has made the transition from 8bit Microchip/Atmel to 32bit ARM and has any advice, I'd love to hear it! I have yet to work on a RTOS as the PIC doesn't have a lot of great options, so I've coded sort of schedulers, my own ADC, SPI, and CAN drivers. I know how to read SFRs and datasheets, but there is a whole generation or two gap here I'm jumping. So anything that comes to mind would be welcome.

4. RTOS. CMSIS or something as I understand it allows cross brand chip use, but at a higher overhead. I haven't looked into this a ton yet. Is there a specific RTOS that you Keil users like over others? I work in automotive but AutoSAR and even OSEK are undesirable for my uses. I'd really like something I could trace through. But I also need to convince the CFO of every purchase, so costs needs to be reasonable.

4. (CAN BUS SPECIFIC) Does anyone work with Keil + Cortex + CAN Bus? Is this a solid system? In this scenario who's driver would I likely start with? Something the mfg puts out? Something Keil has? My own? Is there something else that might be better? Microchip's CAN implementation is so bad, that I really can't imagine anything worse, but I need to find an arc that has first party and community support.

Thanks! J