I am on the 3G plan as well and my phone almost always shows 4G/LTE but the plan is called 3G because the internet speed is limited to what 3G speed would be even though it is on a faster networj
I have an LG G5 as well that I bought from Koodo originally and I tried different ways to get the data working as well. Finally I just did a factory reset and it worked right away, I didn't even have to set up an APN