While Mashrafe, the fastest bowler in the country, is injured severely and is taking a six-month lay-off from cricket - Bangladesh has the vital tour to Sri Lanka in July and lots of problems in front to deal with. Manjural's position is solid, not only because he a left-arm bowler and can generate good pace on any track, but also there is nobody to replace him right this moment.
His long-time buddy Hasibul Hossain lost his rhythm and form and is now almost out of cricket (He didn't play the Premier League because of his shoulder injury). Hasibul's possibility for a comeback in the squad is a far cry. He will be ruled out without a shred of doubt.
Mohammed Sharif may form a junction with Manjural, which is virtually a strong option left for the selectors and probably they would go for that. Bangladesh would hardly settle on for a third seamer in Sri Lanka, keeping in mind two thoughts - firstly those pitches In Lanka would turn out to be barren for average seam bowlers, secondly without Mashrafe they have nothing in their arsenal that they can boastfully call "intimidating" (Mindful that Mashrafe used to bowl at 139/140 km/hour)
A few pacers did well in the domestic first class matches and in the premier league; they can hit the eye. Among the few the names of Alamgir and Taposh Kumar Baiso are pretty prominent. Alamgir bowled some very good overs in Premier league, so did Taposh Baiso - both pulled off with loads of wickets in the league.
Taposh can bowl with pace, keeping a consistent line and length for overs, but lacks variation. He isn't a good mover of the ball, can't bowl swingers frequently, which would give the stalwarts in Lankan order lots of opportunity to handle him quite easily, effortlessly. These two bowlers are short of having another vital feature, which Mohammed Sharif carried out for a good number of times.
Yes, the experience in playing abroad is considered necessary and Sharif (A thinking cricketer) has 6 such experiences in alien Test tracks (The tours in Pakistan, Sri Lanka & New Zealand) where Alamgir and Taposh are to wait for an International exposure. Besides, Sharif is a good combination of Taposh and Alamgir, as he contains Taposh's pace (Almost!) and has the ability to move the ball at both directions alike Alamgir.
As to choose a third pacer, the name of Khaled Mahmud or Mushfiqur Rahman (Both are all rounders) could come into view, but most likely Bangladesh wouldn't run after that possibility - only because they are recognized limited over players.