Today’s midday gainers are Canadian Pacific Railway Limited (NYSE:CP), Rock-Tenn Company (NYSE:RKT) and Marathon Petroleum Corp (NYSE:MPC). On the other end of the stick are Yahoo! Inc. (NASDAQ:YHOO), The Boeing Company (NYSE:BA) and Voltari Corp (NASDAQ:VLTC).

Bill Ackman Pershing Square

Bill Ackman wins with Canadian Pacific

Up +7.25% today, transportation services provider Canadian Pacific Railway Ltd (CP) is our number one midday gainer. Three billionaires tracked by iBillionaire hold positions in the company. The most notable is Bill Ackman, who holds 16 million shares (27.75% of his portfolio). In fact, CP is Ackman’s top holding. Steve Mandel owns 161,000 assets, acquired at an average $92.83, and Richard Chilton has just 2,000 shares – a mere 0.01% of his fund.

Following CP is Rock-Tenn Company (RKT). Its stock price surged +7.04 after the announcement of a $1.66 EPS for the quarter. Billionaire Ray Dalio is the only billionaire tracked by iBillionaire with a position in this company, and a small one at that, as he holds just 30,000 shares.

Last up this Wednesday is petroleum products retailer Marathon Petroleum Corp (MPC), the stock price of which increased +4.65% following an impressive earnings-per-share performance ($2.10). Billionaire Daniel Loeb holds 1.25 million MPC assets, representing 2.01% of his portfolio. And with 70,000 shares acquired at an average $71.80, Dalio is in the mix on this one as well.

Daniel Loeb loses with Yahoo

First on our midday losers list is Yahoo! Inc. (YHOO), , which dropped -8.11%. Billionaire Daniel Loeb owns 16 million shares of the tech giant – one of his top holdings (13.27% of his fund).  Thomas Steyer has a 1.8-million-share position, his assets acquired at an average $18.95 and comprising 1.24% of his portfolio.

Second is Boeing Co (BA), which dipped -6.17%. Guru George Soros hold 231,000 shares of BA, acquired at an average price of $88.13 and representing 0.30% of his portfolio. Dalio has 60,000 shares (0.06% of his holdings).

Voltari Corp (VLTC) fell -6.12% today, earning it the third-place spot on our list of midday losers. With 678,000 shares first acquired in June 2013, Activist investor Carl Icahn has his toes dipped in this one.