Yes, it may be possible on I2C, but would be less efficient, as you would have to code the CAN to I2C gateway, and rewrite your application to use it....
On SPI, you simply have to plug a < 10€ board with for example a MCP2515 CAN driver and a MCP2551 CAN transceiver. Then activate the driver already availlable in the kernel tree, and finally use existing app that are already written using the SocketCAN interface. It can't be made simpler.
About USB to CAN devices, it is another way to do it, but cost a lot more. The cheapest we have at work are about 250€. SocketCAN drivers are already availlable for them in the kernel tree. The one you propose is using its custom format, and still cost 120€.

So having to pay a bit more, or to spend time to develop a new solution, I choose to go to a Wifi to CAN gateway, which will cost less than 100€ and will allow wireless monitoring from ANY device (phone, pc, tablet...) and not only Jolla, using TCP packets, so migrating apps from SocketCAN to TCP will be straightforward.

But SPI would have provided a 10€ only solution with almost no work...