Through the funding of the Federal Aviation Administration's Aviation Weather Research Program, a system for the creation of high-resolution national 3-D radar mosaic was developed at the NOAA/National Severe Storms Lab. The system, which has been running in real-time since June 2004 using base level data from ~140 WSR-88Ds, produces CONUS 3-D reflectivity mosaic grid with 1 km resolution at 5-min update cycle. In early 2006, base level data from 35 radars from Canadian radar network became available to the national 3-D radar mosaic system. A radar reflectivity comparison tool (RRCT) was developed to compare reflectivity data between adjacent Canadian radars as well as between Canadian radar and the adjacent WSR-88D radar. Preliminary 3-D reflectivity mosaics integrating both WSR-88Ds and Canadian radars were developed for a domain covering North Dakota, Minnesota, south Manitoba, Canada and south Ontario, Canada. The mosaic results showed a smooth and consistent 3-D reflectivity grid across the US and Canada radar boundaries. Further, the Canadian radars provide improved low-level coverage due to the lower elevation angles in their volume coverage. The integration of Canadian radar network provides a continuous 3-D radar mosaic with extended coverage north of the US-Canada border. The new 3-D mosaic grids can be potentially beneficial to air traffic controls as well as to convective and winter weather monitoring and predictions along the US-Canada border area.