So some Flys that work are
size 10 to 14 but have used 16 and buddys use smaller 18 20
Black Nat
Red Ant
Mosquitoe
Yellow Cow Dung
Nymphs
Prince
Royal Coachman
Royal Wulff
Royal Humpys
Chironomids
and most small flys if you work the bottom so a indicator with a small weight..Bismuth... size 12 to 16 will work if you put it say 3 to 4 ft down
you could use fly then come up your line and 2 or 3 spilt shots to keep it near the bottom
some flys are pre tyed with line so i just take my line with weight on bottom and make a loop in line then pass the line through the circle i made twice then pull and have a loop on my line up about 16 inches then stick the pre-tyed through the loop and pass the fly through the pre-tyed loop and pull it and it will go on your line and it is easy to take off then as you just push backwards to take pre-tyed off
this will work for Trout in rivers and Grayling /Bulls/Burbot
it is a type of Drift fishing or you can put enough weight to stop and wait fishing..
the Biggest Rocky i know of is 5# 3 oz from Athabasca in Park
but every year people catch 3# and 4# down stream even by Whitecourt
Hope this helps all
remember this is in my opinion
David