Screen resolution and velocity

Hello all!
I'm new at Unity (only 4 month) and have one problem. I've add UI in my game and set "Canvas Scaler" => "UI Scale mode" to "Scale With Screen Size". I typed this for better vision. Maybe, that will help.

Here is the problem:
My objects (enemies for player) have "Rigidbody2d" component and I'm setting fixed velocity for them. When I change resolution in Unity Editor or in my Game Build, the speed of objects become faster with small resolution and slower with bigger resolution.
How can I fix this problem simply?
Cuz, I've already typed this script:
In the beginning of the game I take value of scale from object with Canvas Scaler. Then, I'm multiplying it on objects speed. But, I don't know, is this the best choice?