OK now I have read a lot about these Surecan an No Spill gas cans. The No Spill holds 2.5 gallons (10 L) and closer to the fill up I would need for the i3. The Surecan is 2.2 gallons...slightly smaller. Both have dimensions that will fit in the frunk of the i3 (as pictures and thanks to MHK show).
But I see in the pictures that there are lots of options but like the No Spill for a number of reasons. But I would like to have seen a picture of it upright. The thought of it leaning with its spout off to the side makes me nervous it could possibly leak a substantial amount of fuel if the seal on the top fails.
However, from the dimension of the 2.5 gallon No Spill at 13.5" x 8.3" x 12.5" (L x W x H), it appears that it will fit upright in the frunk. The dimensions inside the frunk that I have measured are: 20.5" x 10.5" x 13 " (L x W x H).
But the height of the frunk is probably higher slightly once the front hood is closed. May a couple of inches higher so I would say the height is closer to 15".
Price wise they are close in price. The No Spill is $63.35 and the Sure Can is $56.90 ($CAN). However, the No Spill recommends an hose extension for another $12.50 (about 8 inches longer).
So I am leaning towards the No Spill...Timothy