I created a analog rpm gauge using the canvas widget of Tkinter and I want to import it in a wx GUI application (as a panel, maybe). Is there any way to do it or I must rewrite this widget in wx?
There is no (simple) way to do that - WxWidgets is an abstraction over different toolkits in different systems, and use different mainloop functions, while Tkinter has its own mainloop - that is to start with.
So  making that work would at leas require:

that you'd setup different threads able to run both mainloops in
paralell,  
finding a way to get Tkinter to render the widget to an
in memory bitmap 
create a custom widget in wx which would render
that bitmap to the screen
and map events on it back to Tkinter, if
it is supposed to respond events

So you are definitely better of writting the widget again.
import a tkinter widget in wxpython application as a panel