There is only one file type that uses the .U10 extension:
UFile 2010 Tax Return
Tax return created with UFile 2010, a Canadian tax preparation program; contains federal Canada tax forms as well as data entered by the user; when completed, the tax return can be printed and mailed or filed electronically using the program's NETFILE feature.
Data from a U10 file may be imported by UFile and other tax software programs.
Updated: March 31, 2012