hover of canvas widget code example
Example: hovering over canvas item tkinter event
You can pass the argument activefill when creating your rectangle.
From effboot.org:
Fill color to use when the mouse pointer is moved over the item, if different from fill.
To do so, replace:
rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red')
By:
rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red', activefill='cyan')