The Republican familiar with the conversations between Cantor and the McCain campaign said Cantor has been asked to turn over documents, but did not know specifically what records were sought.
The person spoke on the condition of anonymity because neither the McCain campaign nor Cantor's office wishes to discuss the running mate selection process.
Cantor through a spokesman declined to comment. McCain spokesman Brian Rogers said the campaign would have "no comment on anything related to the vice presidential issue."
Cantor has been a visible McCain surrogate for weeks, appearing frequently on cable news outlets chiefly to promote McCain's positions on domestic and economic issues.
He has been a forceful critic of Democrat Barack Obama's resistance to lifting the federal ban on oil and gas drilling off the Atlantic and Pacific coasts.
Cantor has strong support among the party's conservatives, perhaps comforting a segment of the base of the GOP that has been reluctant to embrace McCain, who has promoted himself as a maverick.
Cantor is also Jewish and would could bring an important segment of the electorate behind the Republican ticket. If McCain wins with Cantor as his running mate, Cantor would be the nation's first Jewish vice president.
His drawback is his obscurity. Cantor was elected in 2000 from one of Virginia's most conservative House districts. No Democratic challenger has come close to defeating him since, including actor Ben Jones, who played the Cooter character on the "Dukes of Hazzard" television comedy series.