Design vehicle tracking device
There are some SIMCOM modules with GPRS + GPS, for example: SIM968

In addition to GPS, it also supports GLONASS/Galileo/QZSS.

As for the MCU, you will need something more powerful than ATMega328, because 2KB RAM is not enough for multi-threading + GPS code + GSM/GPRS code + CAN + etc. Also it hasn't CAN peripheral. You will need MCU with ARM core. From Arduino line, Arduino Due looks suitable: has 96KB RAM, multiple HW serials, CAN. There is also compatible CAN library here. Also worth looking on STM32F103 (or STM32F407 with Cortex M4) which also can used be with Arduino IDE with some extra effort (STM32 MCUs usually more cost effective than Atmel counterparts, and have higher performance).