As my client acquired by new customer,they looking for possibilities to connect one pardot account with multiple salesfroce instances. is this possible?
The short answer is No.
You cannot connect one Pardot to mulitple SF orgs
However one SF org can be connected to multiple Pardot instances.
You can read more here -> https://help.salesforce.com/articleView?id=000317388&type=1&mode=1