Overlay plan with white background removed on air photo

Going round in circles with what should be a simple task I thought…

I want to overlay the lines and text shown on a plan on top of an air photo.   The plan is available on line and can be downloaded to print but only to print (not as a graphic file). 

I have a scanned version as both a jpg and tif which obviously has the white background, which I would like to remove prior to overlaying it on the photo, which is also available as either .jpg or .tif.  

A transparent layer doesn’t work as the lines and text become illegible.

I have tried erasing the white with magic eraser which works fine and just leaves the lines and text.  However when it’s overlaid on the photo, I need to resize and although the images are of similar physical size (5 and 7 inches wide respectively) I can’t make them line up properly without losing all definition of the lines and text. I must be missing a step in resizing or the file format somewhere but can’t see where.  Also, if the plan is saved as either jpg or tiff and re-opened in any other app the white background is still there.   Any suggestions please ?