Many good responses here, but here is my list of possible issues with your skis (in no particular order)
1) Grind imbedded the edge
2) Hanging burrs not removed with a pass of the Gummy stone
3) Heavy linear grind in the base
4) Bases are concave (edges higher than the base)
5) No base bevel (base and edge perfectly flat) or under beveled for conditions and skiing style
6) Reverse bevel, meaning that there is more base bevel under the foot than at the tips and tails
When a shop tech tunes a ski, they usually first put them on a sanding belt to remove edge burrs from both the side edge as well as the base edge.
This sanding process also prepares the base for the next step of base flattening on the stone grinder and the following grind imprint (the actual finish grind pattern).
If, at this point, the base edge is level with the base itself, and not properly beveled away after sanding, it is easy for the stone to hit the edge when the technician makes the flattening grind passes. This puts the structure right into the steel edge and, since the flattening stone grind is usually linear (running straight from tip to tail), this can make the ski want to run straight and feel like its on rails. Even if the base is flat and the bevels correct, a grind "in" the edge can make a good ski feel horrible when trying to make a turn.
A heavy liner grind in the base can also make a ski want to run straight, even if the edges are polished smooth, but I'm betting this issue is the result of grind marks in the edge.
The only way to remove the structure in the edge is to polish with diamond or ceramic stones moving from a coarse grit to a very fine grit
(something like 220 grit and on down to 400 or even finer). If the technician misses this step, the ski will perform exactly as you mentioned.
Most technicians will not take the time to polish out edges by hand, simply relying on their trim disc (ceramic stone edge machine) and make one pass considering the
job finished; however it is far from being done right as one pass will not totally remove a deep grind imbedded in the steel edge.
These days, de-tuning means something different than it did in the past. We used to de-tune by dulling the tips and tails, however those days are gone and now the skis are
so short it is important to have the entire edge available for carving so the ski can function as designed and not skid into the turn or have the tails wash out. Now, in order to de-tune,
we simply add a small amount of base bevel to the tip to slow any perceived "hooking" and can do the same to the tail for a more friendly release. However for the best performing ski
you want the edge sharp from tip contact point to tail contact point.
Some of the new automated machinery actually can put out a ski with a .75 degree base with 1 degree in the tip and tail. However I like to always finish
skis by hand with diamond and ceramic stones.
You should go back to Canyon Sports and tell them the issue. Perhaps they had a rookie tuner or one who is not well trained, but you can
be sure they want you to be happy and they want to know if their work is coming out inferior.
In the future, select a shop where you know exactly who will be tuning the skis and know that tuners ability. If you hand the skis over the counter and watch
them disappear into the backshop to be tuned by "just anyone" then you take the chance that the tech might not know his trade and the results will vary greatly.
I am sure there are more, but here is my short list of favorite Utah Shops where you can fully trust their work:
Alpine Sports Ogden Utah
Wildrose Ski Shop, Salt Lake City
Rennstall Service Center Park City