When big-screen pairings are dreamt up in Hollywood, it's safe to say not too many expected to ever see Seth Rogen (2012's "Take This Waltz") and Barbra Streisand (2010's "Little Fockers") starring in a mother-son road comedy from Paramount Pictures. One's persona is that of a pot-smoking slacker. The other is a regal musical legend whose last lead role was sixteen years ago in "The Mirror Has Two Faces." Against all odds—or maybe because of its odd-couple charm—director Anne Fletcher (2009's "The Proposal") and screenwriter Dan Fogelman (2011's "Crazy, Stupid, Love.") have made the hard-to-imagine not only possible, but also rather endearing. "The Guilt Trip" opens in a screechy, annoying manner, overstuffed with Jewish women laying on the stereotypes as they talk all over each other, but that lasts all of ten minutes. By the time long-time widower Joyce Brewster (Barbra Streisand) is happily jumping at the chance to take to the road with grown son Andrew (Seth Rogen) on a cross-country business trip, it has fallen more comfortably into a formulaic but delectable groove. One of its successes is in never trying to become more than it is.

Andrew is a struggling L.A.-based salesman trying to garner interest in his new creation, an organic cleaning product burdened with the confusingly pronounced name, Scieoclean. Joyce is his mother, a well-meaning nag who lives on the east coast, excitedly counting the days until she gets to see her only child. When Andrew comes for a visit and learns, in a rare heart-to-heart between the two, that his mom once was in love with another man before she married his father, he becomes intrigued. Tracking down the one that got away in San Francisco, Andrew invites Joyce along on his road trip of business meetings, intending to conclude their journey with a surprise visit to her lost love. As predicted, mishaps, misadventures, and some much-needed bonding between son and mother ensue.

If the sight of Barbra Streisand attempting to get her food for free by finishing a ginormous steak dinner at a Texas roadhouse sounds just unlikely enough to be amusing, then "The Guilt Trip" might be right up your alley. The film doesn't shirk its conventions, but embraces them, recalling a lesser but still entertaining "Planes, Trains and Automobiles" at times. Andrew and Joyce uncomfortably meet up with his ex-girlfriend (Yvonna Strahovski) and her new beau (Colin Hanks). They briefly get snowbound and find themselves at a strip club together. When an argument sends Joyce downstairs to the hotel bar, Andrew must protect her from the advances of a truck driver with more on his mind than big rigs. A stop at the Grand Canyon is anticlimactic for them, while a pit-stop in Vegas sends Joyce on a gambling craze. Andrew has a memorable stop at a home shopping network where, against the odds, he puts down all defenses and sells his product the way it should have been sold all along. Of course, there's a falling-out where Joyce discovers the truth about why she was invited on the road trip, but their reconciliation comes just in time for that fateful climax in San Francisco, where Joyce intends to reconnect with her boyfriend from forty or so years ago.

With the exception of a handful of cameos along the way—Adam Scott (2012's "Friends with Kids") and Ari Graynor (2012's "10 Years") pop up for tiny but vital roles near the end—this is a two-person show. Seth Rogen and Barbra Streisand are just about as perfect as perfect can be together, believably playing son and mother in all of its hair-pulling, but ultimately reassuring, intricacies. As Rogen learns to see his mom as so much more than just that woman that raised him and now can't get the eastern and pacific time zones straight when she calls him in the middle of the night, Streisand clearly is having a great time portraying a relatively normal, middle-class character who wears sweats and eats M&Ms in bed. Also pleasing are the lack of Jewish references and clichés; their religion is neither mentioned nor made into a broad joke. Much funnier, anyway, are the sneaky little gags and dialogue exchanges that ring true, like when Joyce runs out of a convenience store and gets into the wrong car without realizing it—as Andrew looks on, tickled by what he sees.

"The Guilt Trip" is airy fare, and a line of good actors are wasted in head-scratching bit parts that give them nothing of interest to do, but by the conclusion it has also earned a little pathos to go along with its humor and predictable narrative path. It is a foregone conclusion that Andrew and Joyce end the film much closer and with a deeper understanding of each other than they start it with, but Rogen and Streisand ensure that this bonding strikes an authentic note. Director Anne Fletcher and writer Dan Fogelman also avert expectations with the third-act San Fran stop; what happens with Joyce's old boyfriend is not what anyone expects, culminating in a neat, touching capper to the scene. If more demanding Oscar bait titles are not what some viewers are looking for this Christmas season, one could do much worse than "The Guilt Trip." Many will be surprised by how much they identify with it.