Greetings,
Next step is mounting the antenna outdoors. Attics are terrible for installations. They weaken signals greatly, create unpredictable signal environments and put your antenna much closer to household interference. The fact that you even decode any US broadcasts is a positive sign in the attic.
FOX and ABC are to weak to "punch through" your roof. Outdoors is the only place they'll be received. Generally anything below 20db in signal strength is off the table in a attic install.
Outdoors may remedy your stronger Canadian signal drop outs too. These may be victim of the unpredictable nature of attic environments.
Trees are also a wildcard. They attenuate (read: reduce) signal strength and when they move in the wind they change the situation which the signal is arriving often slicing and dicing the signals. The result you see is a drop out. As such, homeowners hate this recommendation but either 1) Mount above the trees or B) cut the trees down. The best antenna system in the world cannot perform to it's potential with things blocking the signal.
There are some options such as a tower or being creative with mounting your antenna like this:
Though, the next step is testing outdoors. The HBU44 would've been better to test as recommended by Teleview with as it has a wider beamwith. The Winegard being a great performer may not have that sweet spot where you get both US and Canadian channels to your satisfaction.
Cheers.