The code to copy one bitmap into another is like this:
Rect src = new Rect(0, 0, 50, 50);
Rect dst = new Rect(50, 50, 200, 200);
canvas.drawBitmap(originalBitmap, src, dst, null);
That specifies that you want to copy the top left corner (50x50) of a bitmap, and then stretch that into a 150x150 Bitmap and write it 50px offset from the top left corner of your canvas.
You can trigger drawing via invalidate() but I recommend using a SurfaceView if you're doing animation. The problem with invalidate is that it only draws once the thread goes idle, so you can't use it in a loop - it would only draw the last frame. Here are some links to other questions I've answered about graphics, they might be of use to explain what I mean.
In response to the comments, here is more information:
If you get the Canvas from a SurfaceHolder.lockCanvas() then I don't think you can copy the residual data that was in it into a Bitmap. But that's not what that control is for - you only use than when you've sorted everything out and you're ready to draw.
What you want to do is create a canvas that draws into a bitmap using
Canvas canvas = new Canvas(yourBitmap)
You can then do whatever transformations and drawing ops you want. yourBitmap will contain all the newest information. Then you use the surface holder like so:
Canvas someOtherCanvas = surfaceHolder.lockCanvas()
someOtherCanvas.drawBitmap(yourBitmap, ....)
That way you've always got yourBitmap which has whatever information in it you're trying to preserve.