LOS ANGELES (AP) _ Justin Bieber's court cases on both sides of the U.S.-Canadian border could complicate the pop star's jet-setting ways as his troubles bring more scrutiny by judges and prosecutors,

Legal experts said a decision by Toronto authorities to charge the 19-year-old Bieber with assault on Wednesday makes his legal situation more complicated and difficult to untangle. He is already facing a driving under the influence case in Miami and remains under investigation for felony vandalism in California.

All the cases are in the early stages and it's uncertain whether the Grammy-nominated singer might be convicted of any charges. But if he is, it would impact how judges deal with him, said Stanley L. Friedman, a former federal prosecutor who now practices criminal defense in Los Angeles.

``I think the legal system is much more likely to treat him harshly as somebody who needs to be taught a lesson,'' Friedman said. `'Now he's become a national poster child for being a bad boy.''

Andrew Flier, a criminal defense attorney who has represented sports stars and actors, said immigration issues are likely Bieber's biggest problem at this point. If the singer is convicted, he could get closer scrutiny when traveling from his homeland of Canada to the U.S., where he now lives.

``Multiple convictions even on misdemeanors could be troublesome to the non-citizen,'' Flier said.

Bieber has pleaded not guilty to DUI, resisting arrest without violence and driving without a valid license in the Miami case.

A preliminary toxicology report released Thursday showed that he tested positive for marijuana and the anti-anxiety drug Xanax. Bieber told police after the arrest that he had been smoking marijuana and had taken a prescription drug.

In California, the singer remains under investigation for an egg-tossing incident that left his neighbor's house with thousands of dollars in damage. If Bieber is charged in that case, a California judge may look at him more harshly in light of the Florida and Toronto cases, said Stan Goldman, a criminal law professor at Loyola Law School, Los Angeles.

``The fact that you've got three is a heck of a lot worse than one,'' Goldman said.

Bieber has not addressed the vandalism claim in California, and his attorney Howard Weitzman has said the singer's legal team believes their client is innocent in the Toronto case.

Friedman agreed and said Bieber's other cases might make it more likely that he will be charged in Los Angeles. Prosecutors have a lot of discretion in how they pursue cases, and a judge has limited influence in the early stages about what deal Bieber might be offered or whether the case goes forward.

If Bieber is convicted in any of the cases, he would lose the benefit of the doubt that judges often give first-time offenders, Goldman said.

For example, a judge could opt to keep Bieber on a long probation sentence to make sure he stays out of trouble, Goldman said, citing the case of Lindsay Lohan.

The actress has been on some form of probation constantly since taking a plea agreement after being arrested twice for driving under the influence and drug possession in 2007.

Numerous stars have had their international travel curtailed because of legal trouble, and attorneys said the U.S. and Canada both view drug offenses harshly when deciding immigration issues.

A Los Angeles judge restricted Lohan's travel during the height of her probation. Japan blocked the entry of The Rolling Stones over drug convictions and in 1980 deported Paul McCartney for marijuana possession at Narita International Airport. In 2010, Japan blocked Paris Hilton from entering the country just days after she pleaded guilty to a misdemeanor drug charge in Las Vegas.

R&B star Chris Brown must still have his international travel approved by a judge overseeing his probation for a 2009 attack on then-girlfriend Rihanna.

David S. Kestenbaum, an attorney who represents a paparazzo charged with driving recklessly to obtain shots of Bieber, said the pop star's troubles will likely affect his travels.

Kestenbaum agreed with other experts who said Bieber's chances of being deported from the U.S. remain low but said that doesn't mean the pop star will quickly clear customs if he's convicted. Agents could scrutinize Bieber and his entourage more closely in screenings for narcotics or other contraband, and some countries may require him to obtain a special visa, Kestenbaum said.



Anthony McCartney can be reached at http://twitter.com/mccartneyAP .