Good news, I now have USB and CAN transmit working! The development setup looks a bit like this.
Right now I'm using CDC-ACM for USB. This emulates a serial terminal, and is really easy to develop applications for. It's also cross-platform, and does not need drivers on many systems.
For CAN, I'm using a Kvaser Memorator to test with. This device provides a CAN to USB bridge. The green PCB in the middle is a CAN terminator, which puts a resistance across the differential bus to terminate it.
The launchpad sits on top of a little Boosterpack, which just has the MCP2551 CAN transceiver on it. This transceiver operates at 5 V, which is available from USB. Fortunately, it will accept the 3.3 V input from the MCU, and the MCU is tolerant up to 5.5 V. This means no level shifting is required.
Currently, the device can go onto the bus, set its bit rate, and transmit messages. Next up is working on receiving messages.