As Derrel said they are similar in overall performance. Looking at the measurement graphs ISO performance is about the same. Dynamic range the Nikon has a lead until the higher ISO settings. But at low ISO where you would normally shoot around the advantage is quite noticeable. Tonal range they are pretty much even with just slight lead to the Nikon. And color sensivity the Nikon has an advantage through the whole range. The Nikon scores higher in ISO due to it being able to go to ISO 25,600. But that's not something you would use except in a very extreme case.
The Nikon is a newer design by a year and a half. The Canon's have the advantage of having 14 bit processing over the Nikons 12 bit. The Canons have a little bit better weather sealing. And have slightly better rear monitors. The Canon's have in camera exposure bracketing the Nikon does not. The Canon's have more AF points 19 to the Nikons 11. Video on the Nikon is just slightly better. From what I have seen the Nikon is $100 less than the Canon's. So, the Nikon has a better sensor. The Canon's have some better features.
I own the previous version of the D3400 the D3300. I carry it as my light weight travel camera even though I have better more capable dslr's. As Derrel said be cautious of what is in the kits. Many sellers are tricky. Also those kits you see with lots of accessories like filters, tripods, cleaing kits, maybe a flash, memory cards. Stay away from them. Most of the items are junk! And some of those kits they take out the manufacturers items and put in cheap knock off items in their place. They look like your getting a lot. But your just paying for junk.