I just realized that it is my LaTeX editor that copies math as unicode, not Canvas that interprets it as unicode.
However, my suggestion in my last reply stands. The Canvas editor should interpret pasted content surrounded by $ or $$ as LaTeX math. For example, "$x=4\cos\left(t\right)$" (without quotes). If I open the "Equation Editor", leave "Directly Edit LaTeX" unchecked, and paste "$x=4\cos\left(t\right)$" (without quotes), it does interpret it as LaTeX. However, it would be useful if the main editor also did so.
Note that the textarea in the "Equation Editor" appears to be read-only by an partial transparent cursor when "Directly Edit LaTeX" is unchecked, but it is still editable. This seems to be cosmetic bug.
Furthermore, it would be absurdly useful is the editor detected pasted LaTeX math even when it is not surrounded by $ or $$. For example, "Q=\left\{ P,Q,R,S\right\}" (without quotes). Though, this is a whole other beast to implement.