Will a 2006 buick lacrosse engine run in a 2003 pontiac bonneville?

Did you use the ECU, ignition switch and key from donor car? And does it crank over and try, or not even turn over?

Will I be able to purchase one because I ended up getting my engine off ebay motors..if not how do I go about fixing the issue so it'll start. It's turning over but it's like the computer is not readin that it wants to start. I kinda need to know what can be done because I have to much money wrapped into this. Thanks

As long as it's a 3.8 ltr, 6 cyl, Series II engine, it should be compatible. I had my 2000 SE motor replaced in 2010 with a Buick motor (I forget what model now), and it worked fine. Did you replace the water pump? Was told this almost always needs replaced in conjunction with engine swap...