By Alastair Sharp

TORONTO (Reuters) - Research In Motion's PlayBook, the long-awaited response to Apple's iPad, goes on sale in the United States and Canada on Tuesday in a launch RIM desperately hopes will win the hearts and minds of consumers.

The stakes could not be higher for the Canadian company, whose BlackBerry smartphone once reigned supreme but has struggled to compete since Apple's iPhone and a slew of devices running Google's Android entered the fray.

The launch has not been helped by reviews, which have panned the WiFi-only tablet computer for lacking RIM's trademark email and organizer applications. However, retailers including Staples and Best Buy say solid pre-orders for this week's launch suggest pent-up demand for a capable alternative to the iPad.

Some 20,000 stores across the United States and Canada will stock the PlayBook at launch, and it will also be sold directly to enterprises.

Some say it is unfair to even stack the contenders up against the iPad, which single-handedly made the tablet market a reality last April. Apple sold almost 15 million iPads in 2010; RIM is expected to move 3 million PlayBooks in a similar window in 2011, according to 18 analysts polled by Reuters.

"It's not going to be in the same league as the iPad," said Al Hilwa, a Seattle-based analyst at IDC. "The question is will it sell more than the Xoom but less than the Galaxy," for example, he said, referring to Android-based tablets from Motorola Mobility and Samsung.

Underscoring the challenges in whipping up the type of buzz typical of an Apple launch, Staples Canada ditched plans to open its doors at midnight for a more sensible 7 a.m. opening.

But analysts say RIM's Playbook should stay in the hunt, even if it gets off to a slow start as it overhauls its creaky platform with the QNX operating system it acquired last year.

Gartner, a research outfit focused on technology, estimates one in 10 touchscreen devices sold in 2015, or some 30 million, will be powered by QNX, which will likely also find its way onto its smartphones in the next 12 months.

That would place it third behind Apple at almost half the market and Android at just under 40 percent, leaving little room for Hewlett-Packard's soon-to-launch WebOS tablet and completely ignoring a possible Windows tablet platform.

CARRIER EXCITEMENT LIMITED

RIM made its name among a white-collar crowd when mobile email was a novelty and has been slow to broaden its appeal.

And in its current setup, the PlayBook's prime audiences are the 60 million-odd active BlackBerry users worldwide and corporate IT managers who appreciate the reliance on a BlackBerry for access to corporate data. RIM expects large businesses to buy shipments in "the tens of thousands."

Without a cellular connection, carriers such as Verizon are unlikely to get too excited as they stand to gain little from selling a tablet without a data plan, although the cost savings may attract consumers.

In Canada, carrier Telus aims to set itself apart by offering PlayBook buyers 45-minute sessions with specially-trained staff to explain the device. But Telus' attention is also split; Motorola's Xoom launches there the same day.

Cellular-connected PlayBooks are due out mid-year.

For the boy in every businessman, RIM has stolen a sheet out of the iPad's playbook, teaming up with Electronic Arts to ship its tablet with the car-racing game 'Need For Speed: Undercover'.

(Reporting by Alastair Sharp, editing by Bernard Orr)