GPS Blending (aka Dual GPS) over CAN bus

ArduCopter
,
1

I am curious if there is any significant advantage over another setup in GPS blending.

  1. Dual CAN ports
  2. Single CAN port + I2C Board.

A few advantages I see using option 1 are less weight, space usage (I2C Board), and ease of identifying Node ID to the physical GPS for position offset.
Why are most GPS manufacturers recommending two CAN ports setup?

  1. Holybro
  2. Cubepilot

Does series or parallel performance difference exist by a single driver or dual driver?

If users have a third CAN peripheral device, what is the best approach for the users making the connection?