According to XMF the prodcution crew for X3 may be returning to Hatley Castle which was the same used in X2 as the X-Mansion.
"Sources say that X-Men 3 will start principal photography at Hatley Castle (Royal Roads University) in Victoria, Canada at the end of this month!"
Hatley Castle
"The building will serve as Xavier's School for The Gifted. Though the shoot is expected to start in last week of July, it's believed that some photography (2nd-Unit) could possibly start before that.This a reunion of sorts for cast and crew because the was location was also used for X2."
"Filming there is expected to last for approximately 3 weeks. The cast and crew will then move on to Vancouver Film Studios. As we speak, the writers Simon Kinberg and Zak Penn are working around the clock on the script."
Stay tuned to CBM for the latest....