I understand that they are listed as co-requisite. Is it recommended to do both due to difficulty?
Your question doesn't make sense...unless you want people to recommend a hard combination for you to do, which in that case, the answer is yes.
You should do ELEC1111 in your second semester, then do ELEC2134 in the following semester (i.e. 2018 S1).
If you do Elec/CS, then in your first year, you'll need to get through 2x MATH, 2x PHYS, ENGG1000, ELEC1111, 2x COMP. So you can't really do both ELEC courses together unless you delay ELEC1111 until 2018, which I would not recommend since you would not have experienced ELEC in your first year.