I would go with elec/maths but you should do elec/commerce if you really are interested in commerce otherwise it will be really boring and you wont do well even compared to engo courses. Im guessing you initially wanted to elec and then decided to add something on there?
Adding commerce is just if you think you might actually fall back on it later which I can't imagine for myself. As for job prospects you just need to get experience in engineering and I doubt you will get the job just because you did commerce as well. As for business skills and such, you don't need an undergrad commerce degree for that as you can come back later and do something like an MBA or
MBT. Now combining with maths is also a similar thing, it will really help with elec i think since we do the most maths out of all engos. Otherwise if you are a full maths geek then go for it anyway!