2004 Pontiac Bonneville Exhaust Modification

An exhaust specialty shop can help with that. There are often multiple pipe sizes the car could have come with depending on a number of options including engine size. Also, some factory pipes are non-standard sizes. You'll need to crush a larger replacement pipe with the clamps to form a tight seal. Some shops never weld pipes, and some do it regularly. With standard size pipes, the replacement section should seal just fine with a pair of clamps, but if you have an oddball size, most shops will likely only weld the joints for liability reasons. They won't want to chance having a leak that can lead to you getting sick.