Anyways the way I see it...

Direct Involvement = United States, Israel, Britain
Indirect Involvement = Saudi Arabia, Pakistan, Canada

United States = provided needed drills to allow event to happen (Amalgam Virgo 02-1 Red Spins, Amalgam Virgo 01, Vigilant Guardian, Global Guardian, Tripod II, Northern Vigilance, as well as several others), set drill security to lowest level possible that morning to allow for drill hacks (entire operation ran through hacks via prep for Global Guardian allowing for maximum plausible deniability), provided needed access to secure systems (PENTAGON/NORAD/FAA via PTECH as prep for Vigilant Guardian and Global Guardian), purposefully created breakdown in chain of command during event (via a final element of Vigilant Guardian (attack on capitol with break in chain of command) to be used to initiate Global Guardian continuity of government protocols), and then provided all elements of the aftermath cover up (Tripod II, Timely Alert II, MASCAL, AMEC...).
sidenote: The operation was done via CoG and its various branches including Kroll Int, PTECH and MITRE Corp (just to name a few) as well as a small group within the federal government itself in key positions such as Chaney, Rumsfeld, Zakheim to (just to name a few).

Israel = Managed the prep elements of the WTC 1/2 demolition operation (via Gelatin/E-Team/Urban Moving Systems...)

Britain = Managed the prep elements of the Pentagon and WTC7 demolition operations (via AMEC construction "bomb mitigation" renovations)

Saudi Arabia = Used by US for wanted public cover patsy's (and backup fall guy in worst case situation).

Pakistan = Used by US for wanted patsy payment/paper trail (and backup fall guy in worst case situation).

Canada = Used by US to allow drill hacks to switchover to "live events" to ensure the event went down without being interception in any way (via the drill Vigilant Guardian, which put Canadian NORAD in charge of the entire Eastern sector of US air defense during the attacks).
sidenote: Canada was the Blue Team (defenders), US was the Red Team (attackers).

Anyways, just my 2 cents...